Waterproof Armband Heart Rate Monitor. The nucleus of our health and fitness is the heart. Being able to accurately monitor, measure, record and transmit heart rate data over an extended period of time is essential to maximizing one’s workout - whether it be running, cycling, swimming or working out in the gym. This is the very essence of the Scosche Rhythm24™ waterproof heart monitor. This next-generation, armband heart rate health and fitness device is highly accurate, packed with outstanding features and very comfortable to wear, so you can ditch those chest strap devices and now workout longer, in more places and in maximum comfort.