EddystoneTLM

EddystoneTLM is a telemetry frame type defined by Google for the Eddystone family of Bluetooth Low Energy beacons. It is used to broadcast health and status information about the beacon itself, rather than conveying a URL or an identifier. The TLM frame is carried in the Eddystone service data (UUID FEAA) and can be transmitted alongside other Eddystone frame types such as UID, URL, or EID.

The frame structure begins with the frame type identifier for Telemetry (0x20) followed by a version field (commonly 0x00 for the standard TLM frame). The remaining fields convey the beacon’s telemetry data in a fixed layout: battery voltage as an unsigned 16-bit value in millivolts; temperature as a signed 16-bit value in a fixed-point 8.8 format representing degrees Celsius; a 32-bit unsigned advertising PDU count since power-up; and a 32-bit unsigned time since power-up in units defined by the specification. Battery voltage and temperature are intended to help operators monitor device health, while the counters provide basic timing and activity metrics.

Usage and considerations: EddystoneTLM is designed for maintenance and monitoring applications. The data is broadcast publicly via BLE advertisements without encryption, so it is visible to any listening device. Implementations may vary in how frequently TLM frames are emitted and whether they are enabled on a given beacon. As with other Eddystone frames, readers decode the data to extract the telemetry fields for diagnostics or analytics.

See also: Eddystone, Eddystone UID, Eddystone URL, Eddystone EID, Eddystone service data.