Motor hair trimmers, also known as hair clippers, work by using a small electric motor to move a series of sharp blades back and forth rapidly. When the trimmer is turned on, the motor drives a small cam that causes a blade to oscillate back and forth against another stationary blade. The oscillation of the blades creates a cutting action that trims hair as it passes through the space between the two blades.

The length of the hair that is cut is determined by the distance between the two blades. Many trimmers come with adjustable blades that can be moved closer together or farther apart, allowing the user to control the length of the hair that is trimmed.

Hair trimmers also often come with attachments, such as combs, that can be clipped onto the blades to further control the length of the cut. These attachments typically have varying lengths, allowing for a wide range of cutting options.