Accelerometer

An accelerometer is a sensor that measures proper acceleration, the change in speed plus the pull of gravity, along one or more axes. Phones and wearables use tiny MEMS accelerometers etched in silicon, with a microscopic mass whose movement is measured electrically.

Why it matters

Because gravity counts, a device at rest on a table reads about 9.81 m/s squared (1 g) along the vertical axis. That is how a phone knows which way is down and rotates its screen. Accelerometers also count steps, detect drops or crashes, wake a device when you pick it up, and enable tilt controls in games.

They cannot measure rotation well, and integrating acceleration to estimate position quickly accumulates error. For this reason they are usually combined with a gyroscope in an inertial measurement unit (IMU), sometimes with a magnetometer too.

Example

Raw output for a phone lying flat might look like this:

x: 0.02  y: -0.01  z: 9.81   (m/s^2)

Tilt it on its side, and the 9.81 moves to the x or y axis. A sudden spike of several g followed by stillness can be interpreted as a fall.

Common mistakes

• Using raw acceleration to calculate distance traveled.
• Forgetting to separate gravity from motion when you need only movement.
• Ignoring sensor noise and calibration offsets.

Related

• Gyroscope
• GPS
• VR headset
• SoC

This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.