The hidden sensors in your phone, explained

Short answer: a typical Android phone carries five or six small sensors that constantly measure how it moves, which way it faces, and what is around it. You use them every day without noticing.

Accelerometer

Measures movement and the pull of gravity. It knows when the phone is tilted, shaken, held upside down or lying face down, and it powers screen rotation and step counting.

Gyroscope

Measures how fast the phone is turning. Combined with the accelerometer it tracks smooth rotation, which is why it is used for panoramas and motion controls in games.

Magnetometer (compass)

Senses the Earth's magnetic field so the phone knows which way is north. Map apps use it to point the blue arrow the way you face.

Proximity sensor

A tiny infrared sensor at the top edge that detects something close to the screen. It turns the display off when you hold the phone to your ear during a call.

Ambient light sensor

Measures how bright the room is and drives auto-brightness. Cover it or walk into a dark room and the reading drops close to zero.

How to tell what your phone has

Phone spec pages list sensors, but the quickest way is to try them: rotate the screen (accelerometer), open a compass (magnetometer), or cover the top edge during a call (proximity).

Try them as puzzles

Tiltwit turns these sensors into brain teasers: tilt to one side, spin around, point north, cover the top edge, find darkness. It needs no camera, microphone or location permission, and lets you skip any box your phone has no sensor for.

Where is the proximity sensor on my phone?

Near the top edge of the screen, usually next to the front camera. It is what turns the screen off when you hold the phone to your ear.

Do all phones have a gyroscope?

Most mid-range and flagship phones do, but some budget phones skip the gyroscope or the light sensor to save cost.

Do sensor apps need special permissions?

No. Motion, proximity and light sensors can be read without a permission prompt. Camera, microphone and location are different and do need permission.