Answer : Accelerometer detects the changes in velocities.
Explanation :
We know that the velocity of an object is defined as the rate of change of displacement. Velocity is a vector quantity i.e having both magnitudes as well as direction.
The rate of change of velocity of a body is called its acceleration. If u is the initial velocity and v is the final velocity of a body. Then the relation for acceleration is :
A device that detects the acceleration (changes in velocity) are Accelerometer. It finds the magnitude and direction of proper acceleration.