An accelerometer is an integrated, built-in module or circuit that accurately detects and measures the acceleration and motion of the application it is attached too. The type of measurement they measure is the rate of velocity change in an object. They commonly measure in G-forces (g) or in meters per second squared (m/s2).
This particular type of sensor is used to measure static (gravity) or dynamic forces (vibration and motion) in acceleration. An accelerometer can measure acceleration with up to three axis units.
These acceleration sensors usually contain internal capacitive plates, some are fixed whilst others are attached to very small springs. These internally move as acceleration forces are happening on the sensor. When these plates move, the capacitance changes between them and from these changes, the acceleration can be determined.
Another type of accelerometer, is a Piezoelectric Accelerometer. These sensors contain minuscule crystal structures that output electrical charge if they ever fall under any mechanical stress, in this instance the stress would be acceleration.
Did you know that a single G-force on planet earth amounts to 9.8 m/s2? This figure can vary, depending on elevation and will be different on other planets because of the difference in gravitational pull.