An electronic leash is the pairing (“leashing”) of one or more wireless devices to a host device that allows the user to find misplaced or out-of-sight objects by activating the host device such that the “leashed” object identifies itself. The system is identical in concept to a key pager, but offers multiple codes that allow a single user-operated device to send codes to a large number of objects. Leash systems generally also offer a form of distance measurement that raises an alarm if the leashed object travels more than a selected distance from the operator.
Modes of operation
The concept may be implemented by various vendors in different ways. A code transmission in conjunction with a distance measurement raises an alarm as soon as a predetermined distance between the paired devices is exceeded. Receivers may be born by the owner of an object, whereas the other transmitting item gets attached to the object for virtually leashing it to the owner.
The transmission distance is adjusted to the intention of keeping the leashed object in contiguity to the bearers body or workdesk or mobile workplace environment, that is a distance usually as short as the visually controlled ambience, i.e. no more than about five metres.
There are four different concepts available for implementing the required distance to raise the alarm:
- conventional RSSI concept as defined by the WLAN IEEE 802.11 and Bluetooth IEEE 802.15.1 standards
- transmission power variation without breaking connection
- transmission power variation provoking breaking connection
- transmission power polarisation segregating direct and indirect path signalling
The four options make use of various physical phenomena and thus offer a variety of signal processing to overcome
- multipath propagation,
- crinked and direct paths
- multipath fading and
- excess reach of nearby colliding transmitters
- higher populations of transmitters.
Two factor concept fails if both items get lost at the same time without raising alarm or one of the batteries is below operational stage or one item is simply inactive.
Basic electronic gadget is a wireless token that communicates with a counterpart attached to the object to be leashed wirelessly. User guides for mode of operation recommend to bear a very light designed alarm token with a necklace, a wristband or similarly directly bound to the body.
After initially pairing the chosen two wireless token devices with each other or one of that type with a distinct mobile phone or smart phone, either one or both raise an alarm when exceeding the set distance. As long as the two items are in reach of the wireless link, the metrics may be applied to support retrieval. After the reach of the wireless link is exceeded, there is no chance to make use of the signalling for retrieval of the lost object.
Advanced solutions offer communications with GSM or LTE mobile phone of any brood, thus requiring just one transmission unit and using the phone as the receiver. However, none of the leashing functions makes use of the networking function of the mobile phone.
The electronic leash is sensitive to a set distance, whereas the concept of the electronic key pager or electronic key fob just responds to any received and properly coded signal when emitted and disregarding variation in dístance.
Object leashing works with the phone at hands working as a receiver. Mobile phone leashing works the other way round. Then the receiver is born with the owner, whereas the phone as transmitter gets virtually leashed. A mandatory feature beyond frequency and modulation discrimination is a code selectivity to prevent from responses to any received signal.
Currently some similar applications are offered:
- Initial pairing of items
- Alarm on separation of paired items
- Forwarding phone ringing
- Forwarding motion detection
- Alarm on low battery condition
- Alarm on key break attack
- Notification on similar nodes transmitting in vicinity
Possible combinations depend on the application on the phone.
Transmission power of the wireless token for the object may be very low in the 1 mW range, as just the distance between the bearer and the item to be leashed shall be bridged. That is a level causing no harm in any environment and electromagnetic interference to sensitive, i.e. medical devices may be neglected.
With highly advanced communication protocols, as with Bluetooth V4.0 low energy protocol, the battery exhaust is significantly lower than with other modes of operation in WPAN (IEEE 802.15) or WBAN (IEEE 802.16) standards.
Respective power consumption with the receiver depends on the mode of communication. With international standard WLAN (IEEE 802.11) and with industrial standard Bluetooth V2.0 (international standard IEEE 802.15.1) the battery of the phone used as receiver may be exhausted much faster than without leashing. Power consumption with the mobile phone unit is comparable to wireless headset operation. However, for phones with better advanced standard Bluetooth V4.0 low energy protocol has just started in 2011Q2 and or future international standard WBAN (IEEE 802.16) will not be in market before 2012 after publishing the new standard.
All known other approaches are either proprietary or just industrial standard, as e.g. ZigBee, ANT of others, hence requiring special pairing of transmitter and receiver resp. Clear specification of battery wear is not published with all known vendors' offerings.
The owner of any mobile phone still shall keep addicted to the basics: Written down IMEI, MEID or ESN number (as generally printed on a sticker placed by manufacturer under the battery of any phone) kept somewhere safe. That is a unique identifier to be taken as a proof of ownership in case of loss. The other is written down PIN code, super PIN code etc. to be kept safely far apart from the phone. And finally, it helps to remember from safely kept notice the own phone number, the subscribers password and the service phone number of the provider.
Informal self determination
The offered service as e.g. with Apple(R)'s products for tracking the current whereabouts of potentially lost items always includes the permanent tracking of the bearers' whereabouts as a severe limitation to informal self-determination beyond the legal requirements yet set for the telephone network operators.