We sometimes get asked “What is iBeacon Technology?”. In terms of the beacon itself, iBeacon doesn’t imply much. The underlying Bluetooth does most of the hard work. iBeacon is only one of many possible formats of standard Bluetooth advertising.
The iBeacon advertising consists of three identifiers UUID, major and minor. We have an article explaining how these are usually set up.
The more useful functionality is in iOS itself. Apps can declare an interest in particular beacons and be triggered even when the app is not running. The triggering is usually used to cause a notification on the phone that the user can tap on to do more. If the app is already open, it can look for beacons and display appropriate app content.
Android may also trigger and scan for iBeacons but this is in the context of scanning for Bluetooth advertising as opposed to specific iBeacons.