|Industry||Digital contact tracing|
|Compatible hardware||Android & iOS smartphones|
|Physical range||~10 m (33 ft)|
The (Google/Apple) Exposure Notification (GAEN) system,  originally known as the Privacy-Preserving Contact Tracing Project, is a framework and protocol specification developed by Apple Inc. and Google to facilitate digital contact tracing during the COVID-19 pandemic. When used by health authorities, it augments more traditional contact tracing techniques by automatically logging encounters with other notification system users using their Android or iOS smartphone. Exposure Notification is a decentralized reporting based protocol built on a combination of Bluetooth Low Energy technology and privacy-preserving cryptography. It is used as an opt-in feature within COVID-19 apps developed and published by authorized health authorities. Originally unveiled on April 10, 2020, it was first made available on iOS on May 20, 2020 as part of the iOS 13.5 update and on December 14, 2020 as part of the IOS 12.5 update for older iPhones. On Android, it was added to devices via a Google Play Services update, supporting all versions since Android Marshmallow.
The Apple/Google protocol is similar to the Decentralized Privacy-Preserving Proximity Tracing (DP-3T) protocol created by the European DP-3T consortium and the Temporary Contact Number (TCN) protocol by Covid Watch, but is implemented at the operating system level, which allows for more efficient operation as a background process. Since May 2020, a variant of the DP-3T protocol is supported by the Exposure Notification Interface. Other protocols are constrained in how they operate as they have no special privilege over normal apps. This leads to issues, particularly on iOS devices where digital contact tracing apps running in the background experience significantly degraded performance. The joint approach is also designed to maintain interoperability between Android and iOS devices, which constitute the sheer majority of the market.
The ACLU stated the approach "appears to mitigate the worst privacy and centralization risks, but there is still room for improvement". In late April, Google and Apple shifted the emphasis of the naming of the system, describing it as an "exposure notification service", rather than "contact tracing" system.
Typically digital contact tracing protocols have two major responsibilities: encounter logging and infection reporting. Exposure Notification only defines encounter logging which is a decentralized architecture, with the majority of the infection reporting, currently it is centralized, being delegated to individual app implementations.
To handle encounter logging, the system uses Bluetooth Low Energy to send tracking messages to nearby devices running the protocol to discover encounters with other people. The tracking messages contain unique identifiers that are encrypted with a secret daily key held by the sending device. These identifiers change every 15–20 minutes as well as Bluetooth MAC address in order to prevent tracking of clients by malicious third parties through observing static identifiers over time.: 02:51:10
The sender's daily encryption keys are generated using a random number generator. Devices record received messages, retaining them locally for 14 days. If a user tests positive for infection, the last 14 days of their daily encryption keys can be uploaded to a central server, where it is then broadcast to all devices on the network. The method through which daily encryption keys are transmitted to the central server and broadcast is defined by individual app developers. The Google-developed reference implementation calls for a health official to request a one-time verification code (VC) from a verification server, which the user enters into the encounter logging app. This causes the app to obtain a cryptographically signed certificate, which is used to authorize the submission of keys to the central reporting server.
The received keys are then provided to the protocol, where each client individually searches for matches in their local encounter history. If a match meeting certain risk parameters is found, the app notifies the user of potential exposure to the infection. Google and Apple intend to use the received signal strength (RSSI) of the beacon messages as a source to infer proximity. RSSI and other signal metadata will also be encrypted to resist deanonymization attacks.
To generate encounter identifiers, first a persistent 32-byte private Tracing Key () is generated by a client. From this a 16 byte Daily Tracing Key is derived using the algorithm , where is a HKDF function using SHA-256, and is the day number for the 24-hour window the broadcast is in starting from Unix Epoch Time. These generated keys are later sent to the central reporting server should a user become infected.
From the daily tracing key a 16-byte temporary Rolling Proximity Identifier is generated every 10 minutes with the algorithm , where is a HMAC function using SHA-256, and is the time interval number, representing a unique index for every 10 minute period in a 24-hour day. The Truncate function returns the first 16 bytes of the HMAC value. When two clients come within proximity of each other they exchange and locally store the current as the encounter identifier.
Once a registered health authority has confirmed the infection of a user, the user's Daily Tracing Key for the past 14 days is uploaded to the central reporting server. Clients then download this report and individually recalculate every Rolling Proximity Identifier used in the report period, matching it against the user's local encounter log. If a matching entry is found, then contact has been established and the app presents a notification to the user warning them of potential infection.
Unlike version 1.0 of the protocol, version 1.1 does not use a persistent tracing key, rather every day a new random 16-byte Temporary Exposure Key () is generated. This is analogous to the daily tracing key from version 1.0. Here denotes the time is discretized in 10 minute intervals starting from Unix Epoch Time. From this two 128-bit keys are calculated, the Rolling Proximity Identifier Key () and the Associated Encrypted Metadata Key (). is calculated with the algorithm , and using the algorithm.
From these values a temporary Rolling Proximity Identifier () is generated every time the BLE MAC address changes, roughly every 15–20 minutes. The following algorithm is used: , where is an AES cryptography function with a 128-bit key, the data is one 16-byte block, denotes the Unix Epoch Time at the moment the roll occurs, and is the corresponding 10-minute interval number. Next, additional Associated Encrypted Metadata is encrypted. What the metadata represents is not specified, likely to allow the later expansion of the protocol. The following algorithm is used: , where denotes AES encryption with a 128-bit key in CTR mode. The Rolling Proximity Identifier and the Associated Encrypted Metadata are then combined and broadcast using BLE. Clients exchange and log these payloads.
Once a registered health authority has confirmed the infection of a user, the user's Temporary Exposure Keys and their respective interval numbers for the past 14 days are uploaded to the central reporting server. Clients then download this report and individually recalculate every Rolling Proximity Identifier starting from interval number , matching it against the user's local encounter log. If a matching entry is found, then contact has been established and the app presents a notification to the user warning them of potential infection.
Version 1.2 of the protocol is identical to version 1.1, only introducing minor terminology changes.
Preservation of privacy was referred to as a major component of the protocol; it is designed so that no personally identifiable information can be obtained about the user or their device. Apps implementing Exposure Notification are only allowed to collect personal information from users on a voluntary basis. Consent must be obtained by the user to enable the system or publicize a positive result through the system, and apps using the system are prohibited from collecting location data. As an additional measure, the companies stated that it would sunset the protocol by-region once they determine that it is "no longer needed".
The Electronic Frontier Foundation showed concerns the protocol was vulnerable to "linkage attacks", where sufficiently capable third parties who had recorded beacon traffic may retroactively be able to turn this information into tracking information, for only areas in which they had already recorded beacons, for a limited time segment and for only users who have disclosed their COVID-19 status, once a device's set of daily encryption keys have been revealed.
On April 16, the European Union started the process of assessing the proposed system for compatibility with privacy and data protection laws, including the General Data Protection Regulation (GDPR). On April 17, 2020, the UK's Information Commissioner's Office, a supervisory authority for data protection, published an opinion analyzing both Exposure Notification and the Decentralized Privacy-Preserving Proximity Tracing protocol, stating that the systems are "aligned with the principles of data protection by design and by default" (as mandated by the GDPR).
Exposure Notification is compatible with devices supporting Bluetooth Low Energy and running Android 6.0 "Marshmallow" or newer with Google mobile services, or iOS 13.5 or newer. On iOS, it is serviced via operating system updates. On Android, it is serviced via updates to Google Play Services (by means of Google Play), ensuring compatibility with the majority of Android devices released outside of Mainland China, and not requiring it to be integrated into an Android firmware (which would hinder deployment), although it is not compatible with Huawei devices released since May 2019 due to the US trade ban on Huawei. Apple and Google released reference implementations for apps utilizing the system, which can be used as a base.
Exposure Notification apps may only be released by public health authorities. To discourage fragmentation, each country will typically be restricted to one app, although Apple and Google stated that they would accommodate regionalized approaches if a country elects to do so.
On September 1, 2020, the consortium announced "Exposure Notifications Express" (EN Express), a system designed to ease adoption of the protocol by health authorities by removing the need to develop an app themselves. Under this system, a health authority provides parameters specific to their implementation (such as thresholds, branding, messaging, and key servers), which is then processed to generate the required functionality. On Android, this data is used to generate an app, while on iOS, the functionality is integrated directly at the system level on iOS 13.7 and newer without a dedicated app. On December 14, 2020, Apple released iOS 12.5, bringing support for Exposure Notifications to older iPhones.
The last information update on the “Exposure Notification Systems” partnership was a year end review issued by Google in December 2020: "we plan to keep you updated here with new information again next year". Nothing has however been issued on the one year anniversary of the launch of the “Exposure Notification Interface” API in spite of important changes on the pandemic front such as vaccination, variants, digital health passports, app adoption challenges as well as growing interest for tracking QR codes (and notifying from that basis) on a mostly airborne transmitted virus.[original research?] The Frequently Asked Questions (FAQ) published document has not been revised since May 2020. Basic support remains provided through the apps store released by authorized public health agencies, including enforcement of the personal privacy protection framework as demonstrated on the UK NHS challenge in support of their contact tracers.
In June 2021, Google faced allegations that it had automatically downloaded Massachusetts' "MassNotify" app to Android devices without user consent. Google clarified that it had not actually downloaded the app to user devices, and that Google Play Services was being used to deploy an EN Express configuration profile, allowing it to be activated from the Exposure Notification section of the Google Settings app on an opt-in basis.
As of May 21, at least 22 countries had received access to the protocol. Switzerland and Austria were among the first to back the protocol. On April 26, after initially backing PEPP-PT, Germany announced it would back Exposure Notification, followed shortly after by Ireland  and Italy. Despite already adopting the centralised BlueTrace protocol, Australia's Department of Health and Digital Transformation Agency are investigating whether the protocol could be implemented to overcome limitations of its COVIDSafe app. On May 25, Switzerland became the first country to launch an app leveraging the protocol, SwissCovid, beginning with a small pilot group.
In England, the National Health Service (NHS) trialed both an in-house app on a centralized platform developed by its NHSX division, and a second app using Exposure Notification. On June 18, the NHS announced that it would focus on using Exposure Notification to complement manual contact tracing, citing tests on the Isle of Wight showing that it had better cross-device compatibility (and would also be compatible with other European approaches), but that its distance calculations were not as reliable as the centralized version of the app, an issue which was later rectified. Later, it was stated that the app would be supplemented by QR codes at venues. A study of the impact of Exposure Notification in England and Wales estimated that it averted 8,700 (95% confidence interval 4,700–13,500) deaths out of the 32,500 recorded from its introduction on 24 September 2020 to 31 December 2020.
In May 2020, Covid Watch launched the first calibration and beta testing pilot of the GAEN APIs in the United States at the University of Arizona. In Aug 2020, the app launched publicly for a phased roll-out in the state of Arizona.
The U.S. Association of Public Health Laboratories (APHL) stated in July 2020 that it was working with Apple, Google, and Microsoft on a national reporting server for use with the protocol, which it stated would ease adoption and interoperability between states.
In August 2020, Google stated that at least 20 U.S. states had expressed interest in using the protocol. In Alabama, the Alabama Department of Public Health, University of Alabama at Birmingham, and the University of Alabama System deployed the "GuideSafe" app for university students returning to campus, which includes Exposure Notification features. On August 5, the Virginia Department of Health released its "COVIDWise" app — making it the first U.S. state to release an Exposure Notification-based app for the general public. North Dakota and Wyoming released an EN app known as "Care19 Alert", developed by ProudCrowd and using the APHL server (the app is a spin-off from an existing location logging application it had developed, based on one it had developed primarily for use by students travelling to attend college football away games).
Maryland, Nevada, Virginia, and Washington, D.C. have announced plans to use EN Express. In September, Delaware, New Jersey, New York, and Pennsylvania all adopted "COVID Alert" apps developed by NearForm, which are based on its COVID Tracker Ireland app. Later that month, the Norwegian Institute of Public Health announced that it would lead development of an Exposure Notification-based app for the country, which replaces a centralized app that had ceased operations in June 2020 after the Norwegian Data Protection Authority ruled that it violated privacy laws.
|Austria||Stopp Corona App||June 26, 2020|||
|Brazil||Coronavírus-SUS||July 31, 2020|||
|Belgium||Coronalert||October 1, 2020 (public)||September 2, 2020 (Pilot phase) |
|Canada||COVID Alert||July 31, 2020||Available in New Brunswick, Newfoundland and Labrador, Ontario, Manitoba, Saskatchewan, Quebec, Prince Edward Island, and Nova Scotia. Alberta and British Columbia have declined its use.|
|Czech Republic||eRouška (eMask)||September 17, 2020||Since version 2.1|
|Denmark||Smittestop||June 18, 2020|||
|Estonia||Hoia||August 20, 2020|||
|Finland||Koronavilkku||August 31, 2020|||
|Germany||Corona-Warn-App||June 16, 2020|||
|Gibraltar||BEAT Covid Gibraltar||June 18, 2020||Based on COVID Tracker Ireland and will interoperate with it.|
|Ireland||COVID Tracker Ireland||July 7, 2020|||
|Italy||Immuni||June 1, 2020|||
|Japan||COCOA||June 19, 2020|||
|Jersey||Jersey COVID Alert||September 21, 2020|||
|Latvia||Apturi Covid||May 29, 2020|||
|Lebanon||Ma3an||July 16, 2020|||
|Netherlands||CoronaMelder||October 10, 2020 (full release)|||
|New Zealand||NZ COVID Tracer||December 10, 2020 (full release)|||
|Norway||Smittestopp||December 21, 2020||Replaced a version of the app that was suspended earlier in the year due to scrutiny from the local Norwegian Data Protection Authority.|
|Philippines||StaySafe.ph||March 29, 2021||GAEN implementation activated in April 2021 |
|Poland||ProteGO Safe||June 9, 2020||Update to existing encounter logging app.|
|Portugal||STAYAWAY COVID||August 28, 2020|||
|Russia||Gosuslugi. Covid Tracker||November 23, 2020||https://play.google.com/store/apps/details?id=com.minsvyaz.gosuslugi.exposurenotificationdroid|
|South Africa||COVID Alert SA||September 1, 2020|||
|Spain||Radar COVID||June 30, 2020 (beta test)|||
|Switzerland||SwissCovid||May 26, 2020 (pilot phase)|||
|Taiwan||臺灣社交距離||May 3, 2021|||
|United Kingdom|| England
|NHS COVID-19||September 24, 2020|||
|Northern Ireland||StopCOVID NI||July 30, 2020||Interoperates with COVID Tracker Ireland.|
|Scotland||Protect Scotland||September 11, 2020||Based on COVID Tracker Ireland and will interoperate with it.|
|United States||Alabama||GuideSafe||August 3, 2020||Targeting University of Alabama students as part of a larger program under the same name.|
|Arizona||Covid Watch||May 28, 2020 (attenuation and dynamic risk testing)
August 19, 2020 (released)
|Targeting University of Arizona in a phased roll-out for the state of Arizona.|
|California||CA Notify||December 10, 2020|||
|Colorado||CO Exposure Notifications||October 25, 2020|||
|Connecticut||COVID Alert CT||November 12, 2020|||
|Delaware||COVID Alert DE||September 15, 2020||Based on COVID Tracker Ireland.|
|Guam||Guam Covid Alert||September 10, 2020||Based on the PathCheck Foundation's GAEN Mobile project|
|Hawaii||Aloha Safe Alert||November 11, 2020||Based on the PathCheck Foundation's GAEN Mobile project|
|Louisiana||COVID Defense||January 22, 2021||Based on the PathCheck Foundation's GAEN Mobile project |
|Maryland||MD COVID Alert||October 10, 2020|||
|Massachusetts||MassNotify||Uses EN Express.|
|Michigan||MI COVID Alert||October 15, 2020 (Michigan State University pilot)
November 9, 2020 (statewide)
|Minnesota||COVIDaware MN||November 23, 2020|||
|Missouri||MO/Notify||July 29, 2021||Targeting Washington University in St. Louis in a phased roll-out for the state of Missouri.|
|New Jersey||COVID Alert NJ||September 30, 2020||Based on COVID Tracker Ireland.|
|New York||COVID Alert NY||September 30, 2020||Based on COVID Tracker Ireland.|
|North Carolina||SlowCOVIDNC||September 22, 2020|
|North Dakota||Care19 Alert||August 13, 2020|||
|Pennsylvania||COVID Alert PA||September 24, 2020||Based on COVID Tracker Ireland.|
|Utah||UT Exposure Notifications||February 16, 2021|||
|Virginia||COVIDWise||August 5, 2020|||
|Washington||WA Notify||November 30, 2020|||
|Wisconsin||WI Exposure Notification||December 23, 2020|||
|Wyoming||Care19 Alert||August 14, 2020|||
|Uruguay||Coronavirus UY||June 15, 2020|||
Some countries, such as France, have pursued centralized approaches to digital contact tracing, in order to maintain records of personal information that can be used to assist in investigating cases. The French government asked Apple in April 2020 to allow apps to perform Bluetooth operations in the background, which would allow the government to create its own system independent of Exposure Notification.
On August 9, the Canadian province of Alberta announced plans to migrate to the EN-based COVID Alert from its BlueTrace-based ABTraceTogether app. This did not occur, and on November 6 Premier of Alberta Jason Kenney announced that the province would not do so, arguing that ABTraceTogether was "from our view, simply a better and more effective public health tool", and that they would be required to phase out ABTraceTogether if they did switch. British Columbia has also declined to adopt COVID Alert, with provincial health officer Bonnie Henry stating that COVID Alert was too "non-specific".
In the United States, states such as California and Massachusetts declined to use the technology, opting for manual contact tracing. California later reversed course and adopted the system in December 2020.
Chinese vendor Huawei (which cannot include Google software on its current Android products due to U.S. sanctions) added a OS-level DP-3T API known as "Contact Shield" to its Huawei Mobile Services stack in June 2020, which the company states is intended to be interoperable with Exposure Notification.
- Sponås, Jon Gunnar. "Things You Should Know About Bluetooth Range". blog.nordicsemi.com. Retrieved 2020-04-12.
- "Exposure Notification API launches to support public health agencies". Google. 2020-05-20. Retrieved 2020-05-21.
- "ExposureNotification | Apple Developer Documentation". developer.apple.com. Retrieved 2020-05-21.
- "Exposure Notifications: Helping fight COVID-19 - Google". Exposure Notifications: Helping fight COVID-19 - Google. Retrieved 2020-07-31.
- "Privacy-Preserving Contact Tracing". Apple. 10 April 2020.
- "Contact Tracing – Bluetooth Specification" (PDF) (Preliminary ed.). 2020-04-10. Archived (PDF) from the original on 2020-04-10. Retrieved 2020-04-10.
- "Apple and Google are launching a joint COVID-19 tracing tool for iOS and Android". TechCrunch. Retrieved 2020-04-10.
- Sherr, Ian; Nieva, Richard (2020-04-10). "Apple and Google are building coronavirus tracking tech into iOS and Android". CNET. Archived from the original on 2020-04-10. Retrieved 2020-04-10.
- "COVID-19 exposure notification settings begin to go live for iOS users with new update". TechCrunch. Retrieved 2020-05-21.
- Miller, Chance (2020-12-14). "Apple releases iOS 12.5 for older iPhones with support for COVID-19 exposure notifications". 9to5Mac. Retrieved 2021-01-05.
- "Apple and Google update joint coronavirus tracing tech to improve user privacy and developer flexibility". TechCrunch. Retrieved 2020-04-26.
- Farr, Christina (2020-04-28). "How a handful of Apple and Google employees came together to help health officials trace coronavirus". CNBC. Retrieved 2020-04-29.
- "Private Contact Tracing Protocols Compared: DP-3T and CEN". Zcash Foundation. 2020-04-06.
- Bogle, technology reporter Ariel (2020-04-26). "Want the COVID-19 tracing app to work properly? Keep your iPhone charged". ABC News. Retrieved 2020-04-26.
- Jason Bay, Joel Kek, Alvin Tan, Chai Sheng Hau, Lai Yongquan, Janice Tan, Tang Anh Quy. "BlueTrace: A privacy-preserving protocol for community-driven contact tracing across borders" (PDF). Government Technology Agency. Retrieved 12 April 2020.CS1 maint: multiple names: authors list (link)
- "How COVIDsafe app tracks people 1.5m from you". Chronicle. Retrieved 2020-04-26.
- "ACLU Comment On Apple/Google COVID-19 Contact Tracing Effort". ACLU. 2020. Retrieved 2020-04-22.
- Morrison, Sara (2020-04-24). "Apple and Google's new contact tracing tool is almost ready. Just don't call it a contact tracing tool". Vox. Retrieved 2020-04-27.
- Google Inc (2020-04-10). "Android Contact Tracing API" (PDF). Google Blog. Retrieved 2020-05-08.
- "COVID-19 - 06/05/2020 12:50:00 – Parliament of Australia". parlview.aph.gov.au. Retrieved 2020-05-06.[permanent dead link]
- "Apple and Google update joint coronavirus tracing tech to improve user privacy and developer flexibility". TechCrunch. Retrieved 2020-04-27.
- "Exposure Notifications verification server". Google Developers. Retrieved 2020-09-01.
- Google Inc, Apple Inc (2020-05-01). "Exposure Notification Frequently Asked Questions Preliminary — Subject to Modification and Extension" (PDF). Apple. Retrieved 2020-05-08.
- "Is Apple and Google's Covid-19 Contact Tracing a Privacy Risk?". Wired. ISSN 1059-1028. Retrieved 2020-04-18.
- Apple Inc, Google Inc (April 2020). "Contact Tracing - Cryptography Specification" (PDF). Retrieved 2020-06-14.
- Apple, Inc (April 2020). "Exposure Notification - Cryptography Specification" (PDF). Apple. Retrieved 2020-05-22.
- "Apple and Google update joint coronavirus tracing tech to improve user privacy and developer flexibility". TechCrunch. Retrieved 2020-05-21.
- Newton, Casey (2020-05-08). "Why countries keep bowing to Apple and Google's contact tracing app requirements". The Verge. Retrieved 2020-05-21.
- Sherr, Ian. "Apple, Google announce new privacy features for coronavirus tracking tech". CNET. Retrieved 2020-05-21.
- "Google and Apple unite to help countries like Australia fix their contact tracing apps". ABC News. 2020-05-21. Retrieved 2020-05-21.
- "Apple and Google release sample code, UI and detailed policies for COVID-19 exposure-notification apps". TechCrunch. Retrieved 2020-09-01.
- Newton, Casey (2020-04-14). "Apple and Google have a clever way of encouraging people to install contact-tracing apps for COVID-19". The Verge. Retrieved 2020-04-15.
- Gebhart, Bennett Cyphers and Gennie (2020-04-28). "Apple and Google's COVID-19 Exposure Notification API: Questions and Answers". Electronic Frontier Foundation. Retrieved 2020-05-21.
- Drozdiak, Natalia (16 April 2020). "Google, Apple Covid-19 Tracking Tech Faces EU Scrutiny". Bloomberg.com.
- ICO (17 April 2020). "Apple and Google joint initiative on COVID-19 contact tracing technology" (PDF). Information Commissioner's Office.
- Gartenberg, Chaim (2020-04-14). "Here's how Apple and Google will track the coronavirus with Bluetooth". The Verge. Retrieved 2020-09-01.
- Bohn, Dieter (2020-04-13). "Android phones will get the COVID-19 tracking updates via Google Play". The Verge. Retrieved 2020-04-16.
- "Apple And Google's Contact Tracing Software Won't Work On Some Huawei Devices". Gizmodo Australia. 2020-05-25. Retrieved 2020-10-07.
- Brandom, Russell (2020-09-01). "Apple and Google announce new automatic app system to track COVID exposures". The Verge. Retrieved 2020-09-01.
- Miller, Chance (2020-12-14). "Apple releases iOS 12.5 for older iPhones with support for COVID-19 exposure notifications". 9to5Mac. Retrieved 2020-12-14.
- "Exposure Notifications: End of year update". 11 December 2020.
- "NHS Covid-19 app update blocked for breaking Apple and Google's rules". BBC News.
- Amadeo, Ron (2021-06-21). "Even creepier COVID tracking: Google silently pushed app to users' phones [Updated]". Ars Technica. Retrieved 2021-06-22.
- "Switzerland, Austria align with 'Gapple' on corona contact tracing". Reuters. 2020-04-22. Retrieved 2020-05-06.
- "Germany flips to Apple-Google approach on smartphone contact tracing". Reuters. 2020-04-26. Retrieved 2020-04-26.
- "HSE Covid-19 tracing app data will be stored on individual devices". The Irish Times. 2020-04-29. Retrieved 2020-05-06.
- "Is it Safe? THE IMMUNI APP Digital Surveillance during the Coronavirus Pandemic". Byline Times / La Stampa. 2020-05-01. Retrieved 2020-05-06.
- "Five questions we need answered about the government's coronavirus contact tracing app". ABC News. 2020-04-16. Retrieved 2020-05-21.
- "SwissCovid App startet in die Pilotphase" [SwissCovid app launched into pilot phase] (in German). 25 May 2020. Retrieved 25 May 2020.
- Neville, Sarah; Bradshaw, Tim; Warrell, Helen (8 May 2020). "UK starts to build second contact tracing app". Financial Times. Retrieved 8 May 2020.
- "UK virus-tracing app switches to Apple-Google model". BBC News. 18 June 2020. Retrieved 2020-06-18.
- Lovett, Tom; Briers, Mark; Charalambides, Marcos; Jersakova, Radka; Lomax, James; Holmes, Chris (2020-07-09). "Inferring proximity from Bluetooth Low Energy RSSI with Unscented Kalman Smoothers". arXiv:2007.05057 [eess.SP].
- "Updates to the algorithm underlying the NHS COVID-19 app". The Alan Turing Institute. Retrieved 2021-06-30.
- O'Halloran, Joe (July 31, 2020). "UK contact-tracing app to be launched 'shortly' as Northern Ireland deploys service". Computer Weekly. Retrieved 2020-07-31.
- Wymant, Chris; Ferretti, Luca; Tsallis, Daphne; Charalambides, Marcos; Abeler-Dörner, Lucie; Bonsall, David; Hinch, Robert; Kendall, Michelle; Milsom, Luke; Ayres, Matthew; Holmes, Chris (2021-06-17). "The epidemiological impact of the NHS COVID-19 app". Nature. 594 (7863): 408–412. Bibcode:2021Natur.594..408W. doi:10.1038/s41586-021-03606-z. ISSN 0028-0836. PMID 33979832. S2CID 234484448.
- "Here's a first look at the government's 'COVID Alert' contact tracing app". MobileSyrup. 2020-07-23. Retrieved 2020-07-24.
- "New COVID-19 notification app rolls out in Ontario". CBC News. 2020-07-31. Retrieved 2020-07-31.
- "UA testing app to trace COVID-19 cases on campus". KOLD News 13. 2020-05-28. Retrieved 2020-05-28.
- "Online apps likely to play a big role in rebooting UA campus for fall semester". Github. 2020-05-28. Retrieved 2020-05-28.
- "UArizona and Covid Watch Launch COVID-19 Exposure Notification App". University of Arizona News. 2020-08-18. Retrieved 2020-08-20.
- "Covid Watch Arizona". App Store. Retrieved 2020-08-20.
- "Covid Watch Arizona - Apps on Google Play". play.google.com. Retrieved 2020-08-20.
- "Bringing COVID-19 exposure notification to the public health community". APHL Lab Blog. 2020-07-17. Retrieved 2020-09-01.
- Walsh, Lauren (2020-08-03). "COVID-19 testing, monitoring system GuideSafe launches". ABC 33/40. Retrieved 2020-08-05.
- "Alabama launches contact tracing app based on Google-Apple API". StateScoop. 2020-08-03. Retrieved 2020-08-06.
- "Virginia Set To Release COVIDWISE App To Public This Week". VPM.org. Retrieved 2020-08-05.
- Wetsman, Nicole (2020-08-05). "Apple and Google's COVID-19 tracking system will make its full US debut in new Virginia app". The Verge. Retrieved 2020-08-05.
- "Virginia Unveils App To Aid Contact Tracing". NPR.org. Retrieved 2020-08-06.
- "ND launches Care19 Alert app to help reduce spread of COVID-19". minotdailynews.com. Retrieved 2020-09-01.
- "Three more U.S. states launching coronavirus exposure warning apps". Reuters. 2020-08-14. Retrieved 2020-09-01.
- Goodin-Smith, Ellie Rushing, Oona. "Contact tracing app tells Pennsylvanians if they've been exposed to coronavirus". Philadelphia Inquirer. Retrieved 2020-10-07.
- Gorey, Colm (2020-10-02). "NearForm contact-tracing apps launched in New York and New Jersey". Silicon Republic. Retrieved 2020-10-07.
- "NIPH starts work on a new solution for digital contact tracing". Norwegian Institute of Public Health. Retrieved 2020-11-17.
- "Uden konkurrence: Netcompany vinder ordren på en ny norsk smittestop-app". Computerworld (in Danish). 2020-10-21. Retrieved 2020-11-17.
- "Archived copy". Archived from the original on 2020-10-23. Retrieved 2020-08-22.CS1 maint: archived copy as title (link)
- "Aplicativo Coronavírus-SUS vai alertar contatos próximos de pacientes com Covid-19" (in Portuguese). Ministério da Saúde. 31 July 2020. Retrieved 31 July 2020.
- "Coronalert", l'application de traçage belge devrait être disponible dès ce mois de septembre" (in French). RTBF. 3 September 2020. Retrieved 27 September 2020.
- "COVID Alert app now operational in Saskatchewan". 650 CKOM. Retrieved 2020-09-18.
- "Few provinces still resisting COVID Alert app as new features under consideration". CBC News. 2020-10-06. Retrieved 2020-10-07.
- "eRouška – chráním sebe, chráním tebe". erouska.cz (in Czech). Retrieved 18 September 2020.
- Kůžel, Filip; Lutonský, Marek. "eRouška 2.0: Co to je, jak se používá a proč se nemusíte bát o soukromí". MobilMania.cz (in Czech). Retrieved 19 September 2020.
- "Smittestop appen downloadet tæt på en halv million gange på den første uge" (in Danish). Ministry of Health (Denmark). 2020-06-25. Archived from the original on 2020-06-28. Retrieved 2020-06-26.
- "The Estonian coronavirus mobile application HOIA is now available for download". Estonian Ministry of Social Affairs. 2020-08-20. Retrieved 2021-09-08.
- "First peek: Finland's Covid-19 contact tracing app". Yle NEWS. 11 August 2020. Retrieved 11 August 2020.
- Bundesregierung. "Corona-Warn-App" (in German). Retrieved 2020-06-16.
- "Scotland's new tracing app: What you need to know about Protect Scotland". BBC News. 10 September 2020. Retrieved 11 September 2020.
- "Beat Covid Gibraltar App - 409/2020". HM Government of Gibraltar. 18 June 2020.
- Wall, Martin; O'Brien, Ciara; Hilliard, Mark (7 July 2020). "Coronavirus: HSE reports 725,000 downloads of new contact-tracing app since launch". The Irish Times. Retrieved 9 July 2020.
- "Covid-19: Tracing app is released for NI". BBC News. 30 July 2020. Retrieved 31 July 2020.
- "Italy launches COVID-19 contact-tracing app amid privacy concerns". Reuters. 1 June 2020. Retrieved 3 June 2020.
- Byford, Sam (2020-06-19). "Japan rolls out Microsoft-developed COVID-19 contact tracing app". The Verge. Retrieved 2020-06-20.
- Jersey, States of. "Government of Jersey". gov.je. Retrieved 2020-10-07.
- "Latvian 'Stop Covid' app first of its kind in the world". lsm.lv. Retrieved 2020-05-20.
- "Stop the spread of the coronavirus, download CoronaMelder".
- "Bluetooth tracing".
- Ranada, Pia (2 April 2021). "StaySafe to use Google Apple Exposure Notifications for contact tracing". Rappler. Retrieved 27 June 2021.
- "Ministerstwo cyfryzacji uruchomilo aplikacje protego safe do sledzenia koronawirusa". Wirtualna Polska (in Polish). 9 June 2020. Retrieved 9 June 2020.
- "App portuguesa de rastreio à Covid-19 já está disponível em Android e iOS". Observador (in Portuguese). 28 August 2020. Retrieved 29 August 2020.
- "Download the app – Every COVID Alert SA app download means more lives saved in SA". SAcoronavirus.co.za. September 2020. Retrieved 2020-09-19.
- Pérez, Enrique (2020-06-30). "Probamos Radar COVID: así funciona la aplicación de rastreo de contactos que usaremos en España". Xataka (in Spanish). Retrieved 2020-07-28.
- "臺灣社交距離App". Taiwan Centers for Disease Control. 2021-05-03. Retrieved 2021-05-03.
- "NHS Covid-19 app: England and Wales get smartphone contact tracing for over-16s". BBC. 24 September 2020. Retrieved 24 September 2020.
- "CA Notify app offers COVID-19 exposure alerts for Stanford community". The Stanford Daily. 2020-12-29. Retrieved 2021-01-13.
- "More than 6 million have signed up for California's COVID-19 alert system". San Diego Union-Tribune. 2020-12-15. Retrieved 2021-01-13.
- "COVID-19 Exposure Notifications Now Available on Your Phone". NBC Connecticut. Retrieved 2020-11-17.
- "Louisiana launches COVID Defense".
- "Louisiana COVID Defense".
- "Maryland Department of Health launches MD COVID Alert". health.maryland.gov. Retrieved 2020-11-10.
- Wetsman, Nicole (2021-06-21). "Massachusetts' COVID-19 exposure notification app auto-installed on Android phones". The Verge. Retrieved 2021-06-21.
- "Spartans Respond with MI COVID Alert". msu.edu. Retrieved 2020-11-10.
- "Coronavirus - MDHHS and DTMB Roll Out COVID-19 Exposure Alert App Statewide". www.michigan.gov. Retrieved 2020-11-10.
- Shamus, Kristen Jordan. "Michigan rolls out new app to alert people of COVID-19 exposure". Detroit Free Press. Retrieved 2020-11-10.
- "COVIDaware MN: Minnesota's free COVID-19 exposure notification app". mn.gov. Retrieved 2020-11-26.
- "Minnesota rolls out new app for COVID exposure alerts". mprnews.org. Retrieved 2020-11-26.
- "COVID-19 Exposure Notifications system launches for university community". medicine.wustl.edu. 29 July 2021. Retrieved 2021-08-24.
- "MO/Notify". play.google.com. Retrieved 2021-08-24.
- "North Dakota announces launch of Care19 Alert app to help reduce spread of COVID-19 as students return". ND Office of the Governor. Retrieved 2020-08-13.
- "Google/Apple Exposure Notification Express Launches in Utah". UT Department of Health. Retrieved 2021-02-17.
- "WA Notify system goes live with COVID exposure notifications for iPhone and Android users in Washington state". The Seattle Times. 2020-11-30.
- "Washington Exposure Notifications - WA Notify". Washington State Department of Health. 2020-11-30. Retrieved 2020-11-30.
- "COVID-19 Contact Tracing App Launches in Wisconsin". Wisconsin Department of Health Services. 2020-12-23.
- "Care19 Contact Tracing Apps". Wyoming COVID-19 Information.
- "Información sobre aplicación Coronavirus UY" (in Spanish). gub.uy. 15 June 2020. Retrieved 15 June 2020.
- Kelion, Leo (2020-05-20). "Apple and Google's Covid-19 'watershed moment'". BBC News. Retrieved 2020-05-21.
- Fouquet, Helene (20 April 2020). "France Says Apple Bluetooth Policy Is Blocking Virus Tracker". Bloomberg.com. Retrieved 27 April 2020.
- "Alberta to adopt national COVID-19 tracing app". Edmonton Journal. Retrieved 2020-08-09.
- "Alberta's contact-tracing app only works on iOS when phone is unlocked, app running in foreground". Global News. Retrieved 2020-08-09.
- Franklin, Michael (2020-11-06). "Alberta will not adopt national COVID-19 Alert app: Kenney". CTV News Calgary. Retrieved 2020-11-17.
- Grubb, Ben (2020-06-28). "'There's no way we're shifting': Australia rules out Apple-Google coronavirus tracing method". The Sydney Morning Herald. Retrieved 2020-09-23.
- "Apple/Google privacy preserving COVID-19 contact tracing. · Issue #10 · AU-COVIDSafe/mobile-ios". GitHub. Retrieved 2020-09-23.
- Volgelstein, Fred; Knight, Will (2020-05-08). "Health Officials Say 'No Thanks' to Contact-Tracing Tech". Wired. Retrieved 2020-05-10.
- "Huawei releases its "Contact Shield" API for COVID-19 contact tracing". xda-developers. 2020-06-08. Retrieved 2020-10-07.
- Official Website (Google)
- Official Website (Apple)
- Announcement (Google)
- Announcement (Apple)
- Overview presentation (Google)
- Technical specifications (Apple)
- Exposure Notification: Frequently Asked Questions (Apple/Google)
- Overview of the version 1.0 of Contact Tracing protocol by Apple & Google
- Overview of the version 1.2 and comparation with version 1.0