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How to test your iPhone's sensors: proximity, barometer, motion and GPS

Each sensor gets its own test in Device Monitor's Diagnostics tab, and each shows live numbers you can judge against what a healthy sensor should read. Cover the earpiece for proximity, walk up a floor for the barometer, go outside for GPS, scan for Bluetooth nearby.

3 min read · Updated 2026-10-06

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Why test one sensor at a time

A sensor fault rarely announces itself with an error - it shows up as a strange symptom instead. The screen stays lit through a whole call. Stairs never register in a fitness app. The blue dot on the map wanders off down the wrong street. Reading the sensor directly tells you whether the hardware actually responds, before you blame an app or pay for a repair that fixes nothing.

iPhone proximity sensor test

The proximity sensor lives near the earpiece and switches the screen off the moment you hold the phone up to your ear. It's also one of the parts most often knocked loose or left disconnected during a screen replacement.

  1. Open Diagnostics > Environment Sensors > Proximity Sensor Test. Monitoring starts on its own.
  2. Cover the top of the screen near the earpiece with your hand.
  3. A working sensor turns the screen off (that is iOS doing it), the phone gives a light tap and, when you uncover it, the card shows Detections increased and the Detection Log lists the time of each event.
  4. Use Stop Monitoring and Start Monitoring to pause and resume.

Nothing happens when you cover the earpiece? Either the sensor's blocked - a screen protector, a case edge creeping over it - or it's actually dead. This test is iPhone only; iPads don't have a proximity sensor at all.

iPhone barometer test

  1. Open Environment Sensors > Barometer & Altitude and tap Start Tracking.
  2. Check the air pressure in kPa. Near sea level it sits around 101 kPa; higher places read less.
  3. Walk up one floor and watch Relative Altitude: it should rise by roughly the height of the floor, about 3 m.
  4. The Pressure History chart shows the readings as they come in.
Example barometer readings
MeasuredShown as
Pressure 101.325 kPa101.3 kPa, Normal
Rise of 9.6 m since Start Tracking9.6 meters / 31.5 feet

The word under the pressure reads Low below 98 kPa, Normal from 98 to 102 kPa, High above that. Altitude is relative to wherever you pressed start, not height above sea level. Devices without a barometer just say so on screen.

Accelerometer test

Motion Sensors > Accelerometer > Start shows X, Y and Z in G, the total G-force, and a Peak. Lying still, a healthy phone reads about 1.00 G - that's gravity, nothing else. Shake it and the total jumps. One quirk worth knowing: the status word says Moving even at a resting 1 G, because of how the app sets its thresholds. Ignore the word, trust the number.

iPhone GPS accuracy test

  1. Go outside, away from tall buildings if you can.
  2. Open Wireless & Location > GPS Accuracy Test and tap Start GPS Test. Allow location when asked.
  3. Read the accuracy in metres, altitude, speed and coordinates. Under 10 m you see Excellent GPS accuracy!; otherwise Moderate accuracy. Move to open area.

The accuracy figure is iOS's own estimate of the radius around the fix - 4.7 m means your real position probably sits within about 4.7 m of the dot on screen. Indoors that number balloons, because the phone falls back on WiFi and cell towers instead of satellites.

Bluetooth and light sensor

  • Bluetooth Scanner > Start Scanning listens for 10 seconds and lists advertising devices, strongest first, with signal in dBm. A reading of -63 dBm counts as Good. Devices showing up at all just proves the radio can receive - the app never pairs or connects to anything.
  • Light Meter uses the front camera. Cover it with a finger and brightness should drop toward Dark; point it at a lamp and it climbs toward Bright. It's a relative percentage, not lux, and should not be trusted past that.

Questions and answers

My proximity sensor stopped working after a screen replacement. Can the app confirm it?
Yes - the Proximity Sensor Test shows whether covering the earpiece gets detected. If the count never moves, the sensor was damaged, blocked, or never reconnected properly during the repair; take it back to the shop.
Why does the accelerometer say Moving when the phone is still?
Gravity is always adding about 1 G, and the app's own threshold counts that as movement. Look at the number instead of the word - about 1.00 G at rest is exactly correct.
Does every iPhone have a barometer?
Most recent ones, yes, but some very old models and a few iPads don't have one. The app just tells you it's not available on those.
Is the light meter in lux?
No. It's a relative brightness percentage from the front camera - good for comparing one spot with another, not a real lux reading.

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