Bluetooth Signal Strength App for iPhone: Check RSSI

What RSSI means

RSSI is just how loud a device's radio sounds to your phone, in dBm, nothing more exotic than that. The numbers run negative, and every 10 dB is a tenfold jump in power, so -60 dBm is ten times stronger than -70 dBm, not merely a bit louder. What you actually get depends on the device's transmit power, the distance, and whatever sits between the two.

How to measure Bluetooth signal strength with Periphery

Tap Scan on the Scanner tab. Each row shows the device's current dBm and signal bars.
Set Sort by to Strongest signal to rank devices from strongest to weakest.
For one device, swipe its row and tap Locate. The screen shows the live dBm in large type and a gauge.
Place the phone or the device where you want to test and wait a few seconds for the reading to settle.
Move one thing at a time, such as distance, height or an obstacle, and compare the steady readings.

How Periphery smooths the reading

Raw RSSI bounces around by several dB packet to packet, it just does. Locate checks the signal 3 to 4 times a second and smooths it so the gauge actually moves steadily instead of twitching: each reading nudges the displayed value a quarter of the way toward the new sample.

A device that jumps from -80 dBm to a steady -70 dBm
Reading	Sample	Smoothed value
Start	-80 dBm	-80.0 dBm
1	-70 dBm	-77.5 dBm
2	-70 dBm	-75.6 dBm
3	-70 dBm	-74.2 dBm
4	-70 dBm	-73.2 dBm

Which is exactly why it helps to wait a beat after any real change in position before writing the number down. Jump too fast and you log the overshoot, not the real value.

From RSSI to distance

Locate also shows an approximate distance, built on the log-distance path-loss formula, distance = 10 ^ ((-59 - RSSI) / 20) metres. It assumes -59 dBm at 1 metre in open space, which plenty of real devices do not quite match.

RSSI and the estimated distance shown
RSSI	Metric	US	Status
-60 dBm	~1.1 m	~3.7 ft	Warm
-68 dBm	~2.8 m	~9.2 ft	Getting Closer
-73 dBm	~5.0 m	~16.4 ft	Getting Closer
-78 dBm	~8.9 m	~29.2 ft	Getting Closer
-83 dBm	~15.8 m	~52.0 ft	Freezing
-88 dBm	~28.2 m	~92.5 ft	Freezing
-93 dBm	~50.1 m	~164.4 ft	Freezing

How to test Bluetooth signal strength for placement

Testing a sensor's spot: phone stays where the receiver will live, move the sensor around, note the steady dBm at each spot it lands.
Testing range: walk away until the status flips to Signal Lost (no packet for 4 seconds), note the last steady value before that.
Testing an enclosure or antenna: same distance, with the case and without it. A few dB of wobble is normal noise; 10 dB is an actual change worth caring about.
Keep the phone's orientation identical across readings. Your own hand and body block signal more than people expect.

Limits

Periphery measures BLE only, nothing else, not classic Bluetooth, not Wi-Fi, not cellular. It also cannot read the signal of a device connected to your iPhone as an audio accessory unless that same device happens to also advertise over BLE. And the free version still caps you at 3 scans in total, this guide included.

Questions and answers

Can I see Bluetooth signal strength in iPhone settings?

No, iOS just does not expose it there. You need a scanner app, Periphery or otherwise, to see the dBm of anything nearby.

What is a good Bluetooth signal strength?

-60 dBm or stronger counts as solid. Between -75 and -90 dBm the link holds but can drop out, and past -90 dBm you are right at the edge of range.

Why do two apps show different dBm for the same device?

RSSI jumps packet to packet, and every app averages it its own way. Periphery's Locate screen smooths the value over time; the scan list just shows the latest raw reading.

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