This is a chest strap which senses your heart-rate and transmits it wirelessly to any Polar-compatible (non-coded) device, such as treadmills and bikes from leading brands like York, Infiniti, and Repco. 

Some equipment comes with a hand-pulse unit which allows the equipment to display your heart-rate, but a chest unit is a much more accurate way to measure your heart rate, and gives you a constant measurement (whereas the hand-pulse only works when you have your hand placed on it).

This unit is the chest-strap (incl elastic band) only, and only works on machines that have in-built receivers.

If you have an existing machine and are not sure whether this chest strap is compatible, please refer to your manuals or call the manufacturer.