It’s an electromechanical device that measures acceleration and tilt angles by using the MEMS (Micro Electro Mechanical Systems) technology, where acceleration is the rate of change of velocity with respect to the time. Acceleration forces may be Static or Dynamic depending upon the way one uses the accelerometer. The change in the acceleration leads to change in the voltage output of the accelerometer.
The alternating magnetic fields are sensed with respective to different motions and then the corresponding motion is converted into an electric signal.
The piezoelectric crystals have the property of generating voltages when they are pressurized. This property is induced in these type of accelerometers to sense the motion and produce corresponding signals.
The two micro structures placed nearby, induces a capacitive value between them whose capacitance value changes according to the motion. So by converting the capacitance value into voltage, the motion can be sensed.
Accelerometers have been extensively used in the field of Automation and Robotics. For example, they are embedded inside the latest versions of laptops (Apple) for preventing the hard disk being damaged by unexpected free fall of them. So basically in these laptops, the hard disk gets switched off automatically whenever accelerometer senses a free fall.
They are also used in Humanoids along with gyro sensors for maintaining the center of gravity positioned in canter of the body. Accelerometers detect vibrations and can be used for testing car engine. They can sense the car crashes and push out the airbags at the right time saving the lives of people in the car.