A heart rate monitor is a device that allows a user to monitor their heart rate whilst exercising. It consists of two elements, a chest strap and a wrist receiver (which usually doubles as a watch). Advanced models additionally measure heart rate variability to assess a user's fitness.

The chest strap has electrodes in contact with the skin to monitor the electrical voltages in the heart (see electrocardiography for more details). When a heart beat is detected a radio signal is sent out which the receiver uses to determine the current heart rate. More expensive monitors send coding signals from the chest strap, this prevent a user's wrist receiver from receiving signals from other nearby exercisers.

There are a wide number of receiver designs, with all sorts of advanced features. These include average heart rate over exercise period, time in a specific heart rate zone, calories burned, and detailed logging that can be downloaded to a PC.