It's the easiest way to measure heart rate during exercise or at rest. The cables are long enough to allow measurements to be made while exercising. Just grab the handles with your hands to get the heartbeat.
The way it works is similar to the systems found on bikes or treadmills in gyms. Electrodes located in the handles record the electrical signals emitted by the heart with each beat.
The sensor has a system that reduces background noise and calculates an average to give the heart rate.