What it means
The advertising interval is the gap between a device’s broadcasts. Short intervals make a device easy to find; long ones save battery and make it appear to flicker in and out of a scan.
A speaker on mains power might advertise every 100 milliseconds. A coin-cell tag stretching a year of battery might advertise once every two seconds or less often still.
This is why a device seems to vanish from a scan and come back. It has not moved and nothing is broken, you are simply between its broadcasts.
It is also why a scan should be given a full minute before you conclude something is not there. Short scans systematically miss low-power hardware.
Related terms
The other pieces of Bluetooth vocabulary that change how you search.
- MAC randomisation: Rotating Bluetooth identifiers
- UWB: Ultra-wideband
- Bluetooth Classic: The older streaming mode
- Find My network: Apple’s crowd-sourced finding
- Unwanted tracking alert: How phones warn you
- Bluetooth scanner for iPhone, Scan tab
- How to find something in the dark, Method
- Full glossary, the complete list
Common questions
Why does a device disappear and reappear in my scan?
It is advertising infrequently to save battery. Wait longer, or wake the device physically if you can reach it.
How long should I scan for?
At least sixty seconds in each position. Anything shorter reliably misses long-interval devices.
In the app: The scan shows this value live for every device around you. Read about Bluetooth Scanner.