A Holter monitor is a battery-operated portable device that measures and tape records your heart's activity (ECG) continuously for 24 to 48 hours or longer depending on the type of monitoring used. The device is the size of a small camera. It has wires with silver dollar-sized electrodes that attach to your skin
A heart rate monitor consists of two parts - a transmitter attached to a belt worn around the chest, and a receiver worn on the wrist like a watch. As the heart beats, an electrical signal is transmitted through the heart muscle in order for it to contract. This electrical activity can be detected through the skin.