Bluetooth Low Energy and beacons: Frugal wireless connections

In short: Bluetooth Low Energy (BLE) transmits small amounts of data with minimal power consumption and enables fitness bands, sensors, trackers and beacons.

In more detail: Classic Bluetooth streams audio and transfers files. Bluetooth Low Energy (from Bluetooth 4.0) is a separate radio method for rare, small data packets: a sensor can run months to years on a coin cell.

In Depth

How BLE works

Devices have two roles: peripheral (sensor, sends “advertisements”) and central (phone, searches and connects). Data is organised in GATT profiles: services contain characteristics (for example “heart rate”, “battery level”) that can be read, written or subscribed to via notify. Range is typically 10 to 50 metres, data rate is low (up to about 2 Mbit/s).

Applications

• Fitness bands, smartwatches, heart-rate straps.
• Trackers such as AirTag and Tile (finding network via other phones).
• Smart-home sensors, door locks, thermostats.
• Medical devices (blood glucose, blood pressure).
• Beacons: small transmitters that constantly send an ID (iBeacon, Eddystone) and trigger apps nearby (indoor navigation, museum guides, payment or check-in actions).
• The Corona-Warn-App used BLE for distance measurement.
• Bluetooth Mesh and LE Audio (Auracast) extend it.

Developing

Microcontrollers such as ESP32 and nRF52 speak BLE. In the browser the Web Bluetooth API (Chrome/Edge, only over HTTPS and with user consent) allows access to devices. Apps use CoreBluetooth (iOS) and the Android BLE API. With apps such as nRF Connect you can inspect devices.

Privacy and security

BLE devices regularly send identifiers; modern devices use changing random addresses so they cannot be tracked. Check pairing and encryption, update firmware, and note that trackers offer warning functions against unwanted tracking (stalking). Switch Bluetooth off when you do not need it.

See also: Bluetooth, Connecting Bluetooth and headphones, ESP32, Smartwatch and fitness band