iBeacon is an indoor positioning system that Apple Inc. calls "a new class of low-powered, low-cost transmitters that can notify nearby iOS 7 devices of their presence." They can also be used by the Android operating system (limited to central-only). The technology enables an iOS device or other hardware to send push notifications to iOS devices in close proximity.
The iBeacon works on Bluetooth Low Energy (BLE), also known as Bluetooth Smart. Bluetooth LE can also be found on Bluetooth 4.0 devices that support dual mode. In a real life scenario it would be more of a location-aware, context-aware, pervasive small wireless sensor beacon that could pinpoint your location in a store: iBeacons could send you notifications of items around you that are on sale or items you may be looking for, and it could enable payments at the point of sale (POS) where you don’t need to remove your wallet or card to make a payment. It could be a possible Near Field Communication (NFC) competitor.
It uses Bluetooth low energy Proximity sensing to transmit a Universally unique identifier picked up by a compatible app or operating system that can be turned into a physical location or trigger an action on the device such as a Check-in on social media.
The beacons come in different formats, including small coin cell powered devices, USB sticks and software versions.
On December 12, 2013, the US patent office released a patent application filed on June 12, 2013, by Apple for an iBeacons Restaurant Ordering & Reservation System. The application covers a unique system whereby a user of an iOS device could be presented not only with options of local restaurants but also wait times and seating availability in real time, and remote and in-restaurant ordering systems that allow customers and staff to place and modify orders. A payment option allows for pre or post payment.
Region monitoring is limited to 20 regions and can function in the background (of the listening device) and has different delegates to notify listening app (and user) of entry/exit in the region - even if app is in the background or phone is locked.
Ranging works only in the foreground but will return (to the listening device) an array (unlimited?) of all iBeacons found along with their properties (UUID, etc..) 
||This section may contain unsourced predictions, speculative material or accounts of events that might not occur. (December 2013)|
In mid 2013 Apple introduced iBeacons and experts wrote about how it is designed to help the retail industry by simplifying payments and enabling on-site offers. With the launch of iOS 7, retailers and other small to medium enterprises will be able to use this Bluetooth 4.0 based technology. On December 6, 2013, it was reported that Apple activated iBeacons across its 254 US retail stores.
In February 2014 Estimote, whose products are built on Apple iBeacons Technology announced an implementation in the Rubens Museum in Antwerp, Belgium 
- iOS devices with Bluetooth 4.0 (iPhone 4S and later, iPad (3rd generation) and later, iPad Mini (1st generation) and later, iPod Touch (5th generation)).
- Android devices with Bluetooth 4.0 and Android 4.3 and later (Samsung Galaxy S3/S4/S4 Mini, Samsung Galaxy Note 2/3, HTC One, Google/LG Nexus 7 (2013 version)/Nexus 4/Nexus 5, HTC Butterfly (aka Droid DNA).
- Macintosh computers with OS X Mavericks (10.9) and Bluetooth 4.0 using the MacBeacon application from Radius Networks.
Although the NFC environment is very different and has many non-overlapping applications, it is still compared with iBeacons.
- NFC range is up to 20 cm (7.87 inches) but the optimal range is < 4 cm (1.57 inches). iBeacons have a significantly larger range.
- NFC can be either passive or active. When using passive mode, the power is sent from the reader device. Whereas altough Passif (bought by Apple Inc.) has worked on reducing the energy consumption, a battery pack is still needed inside iBeacon tag at this time.
- Most smartphones ships with both Bluetooth 4.0 LE and NFC support but at this time, no iOS devices have been released with NFC support.
- "iBeacon Bible". Andy Cavallini. Retrieved 2014-01-01.
- "Apple iBeacons Explained – Smart Home Occupancy Sensing Solved?". Automated Home. Retrieved 2013-12-11.
- "iBeacon- The game changer in InStore Navigation".
- "Submit your iOS 7 apps today.". Apple Inc. June 2013. Retrieved 2013-09-23.
- "SDK will let Android users join the iBeacon party". MobilePaymentsToday.com. 2013-10-11. Retrieved 2013-12-11.
- Bluetooth Smart Marks FAQ
- "iBeacons". Dave Addey. 2013-09-22. Retrieved 2013-12-11.
- "Inside iOS 7: iBeacons enhance apps' location awareness via Bluetooth LE". Forums.appleinsider.com. 2013-06-18. Retrieved 2013-12-11.
- 09 Oct 2013 by James Nebeker and David G. Young (2013-10-09). "Radius Networks". Developer.radiusnetworks.com. Retrieved 2013-12-11.
- Charles Capps - iBeacon in the background
- "Apple launches iBeacon in 254 stores to streamline shopping experience". ZDNet. Retrieved 2013-12-18.
- "Nexus 5 - Google". Google.ca. Retrieved 2013-12-11.
- "Android iBeacon Library". Developer.radiusnetworks.com. Retrieved 2013-12-11.
- "Proximity Services for Businesses and Mobile Applications". Radius Networks. Retrieved 2013-12-11.
Indoor Location Based Services (Indoor LBS) iBeacons www.indoorLBS.com