With the aim of offering a simpler and more comfortable alternative to a chest strap, COROS developed the heart rate monitor for the arm. The heart rate monitor is very precise in its measurement and is barely noticeable on the upper arm. The lightweight strap was designed to be worn on the biceps - it weighs 19 grams including the sensor. The battery lasts 38 hours in activity mode and the HR monitor can be connected to three devices simultaneously via Bluetooth to transmit accurate heart rate data in real time. The HR monitor is compatible with any Bluetooth-enabled device.