What it means
Transmit power is how strongly a device broadcasts. It varies enormously between devices, which is why you can never compare two different devices’ signal readings to each other.
A mains-powered speaker transmits far more strongly than a card-thin tracker running on a rechargeable cell. At the same distance they will show completely different readings.
The rule that follows is simple and important: only ever compare a device against its own earlier readings. Ranking two devices by signal strength tells you about their radios, not their distance.
Thin devices, card trackers, smart rings, some sensors, have low transmit power by necessity and correspondingly short range.
Related terms
The other pieces of Bluetooth vocabulary that change how you search.
- Find My network: Apple’s crowd-sourced finding
- Coin cell: The battery in most tags
- Attenuation: What blocks a Bluetooth signal
- Beacon: A device that only broadcasts
- Advertising interval: How often a device broadcasts
- Get warmer, get colder, Inside Scan
- How to scan a room for hidden Bluetooth devices, Method
- Full glossary, the complete list
Common questions
Why does one device show a stronger signal than another at the same distance?
Because they transmit at different power levels. Signal strength is only meaningful compared against the same device over time.
In the app: The scan shows this value live for every device around you. Read about Bluetooth Scanner.