How Bluetooth RSSI works
RSSI is the received signal strength measured by the phone. Apple’s Core Bluetooth discovery API reports it in decibels. Values are usually negative: a reading closer to zero generally means a stronger received signal.
Follow a trend, not a distance.
Use RSSI as a moving trend. Stand still, collect several readings, move a short distance, and compare. Do not convert one reading into an exact number of feet or meters.
Before you start
- ✓
Compare the same device on the same phone.
- ✓
Keep phone orientation reasonably consistent.
- ✓
Average multiple readings instead of trusting one spike.
- ✓
Move slowly and retest from more than one direction.
- ✓
Use physical inspection to confirm the result.
Search step by step
- 01
Select the target and pause for the signal to settle.
- 02
Remember the rough range instead of a single number.
- 03
Walk a few steps; if readings repeatedly move closer to zero, continue in that direction.
- 04
If they weaken, return to the last stronger point and try another direction.
- 05
Search nearby hiding places once the signal stays consistently strong.
Start with a Bluetooth scan.
Open BLE Detector, choose a likely device and move slowly. A rising signal is a useful clue that you are getting closer.
Download on theApp StoreRequires iOS 17 or later.If it does not appear
Human-body blocking
Your body absorbs 2.4 GHz energy. Holding the phone differently can change the reading.
Walls and reflections
Radio paths bounce and fade indoors, producing strong and weak pockets that are not simple circles.
Different transmit power
Two devices at the same distance can report very different RSSI because their radios and advertising power differ.
Frequently asked questions
Is −40 dBm always closer than −70 dBm?+
For repeated readings from the same device in the same environment, −40 is generally stronger. It still does not prove an exact distance.
Why does the signal jump while I stand still?+
Radio reflections, interference, packet timing, device orientation, and measurement noise all cause variation.
Can RSSI point left or right?+
Not by itself. A typical phone scan measures strength, so you infer direction by moving and comparing.
Start with a Bluetooth scan.
Open BLE Detector, choose a likely device and move slowly. A rising signal is a useful clue that you are getting closer.
Download on theApp StoreRequires iOS 17 or later.