Periphery Unknown Bluetooth device nearby on iPhone: how to check it
Almost always it is harmless: a neighbour's speaker, a smart bulb, a car. What you can do is watch how it behaves. Scan with Periphery, sort by Strongest signal and see whether the same device stays close wherever you go. The Trackers filter can also mark devices that broadcast a public tracker identifier.
Why unknown devices show up
Bluetooth Low Energy devices advertise all day: fitness bands, bulbs, keyboards, sensors, tags. A scanner hears them all, and many have no name, so you see Unknown and a short code.
Check whether it is following you
- Tap Scan at home and note the unnamed devices at the top after setting Sort by to Strongest signal.
- Use Filter by name or UUID to narrow down to the short code of the device you are curious about.
- Go to another room, then outside, and scan again. A device that is only strong in one place belongs to that place.
- If one stays strong wherever you go, swipe its row and tap Locate to see how strong it is right now.
- Give a device you recognise its own name with Rename, so it is not a mystery next time.
What the signal tells you
| Signal | What it usually means |
|---|---|
| -45 dBm or stronger | Within arm's reach |
| -60 dBm | Same room, a few metres away |
| -75 dBm | Another room or across a large space |
| -90 dBm or weaker | Far away or behind walls |
When to worry, and what to do
An unknown device on its own is no reason to worry. If one travels with you from place to place, use the tracking alerts built into your iPhone first. Then tap Trackers to see whether it is marked Possible tracker, for how long it has been Seen for nearby and whether its Signal getting stronger. This is a hint, not proof, and it cannot see every tracker. If you feel unsafe, contact your local authorities.
Questions and answers
How do I find out what an unknown device is?
Does a device that keeps appearing mean it follows me?
Can Periphery see every Bluetooth device?
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