We have already covered the practical aspects of arranging data in profiles, services, and characteristics as part of Bluetooth Low Energy implementation in the peripheral devices in the Chapter 3, Building a Service Explorer App.
In this chapter, we take a break from these discussions and focus on another very interesting and lesser known aspect/parameter related to Bluetooth Low Energy, namely, Received Signal Strength Indication (RSSI), which we will eventually use to detect the proximity/distance (yes, you read that right) to a Bluetooth Low Energy device.
Note that there are BLE devices already available, which support Find Me and Proximity BLE Profiles which can be used to accomplish this task in a very simple and similar manner (Scan|Detect and subscribe to notifications...