Introducing the OHR-31 Optical Heart Rate Sensor, the perfect balance of performance and convenience. This compact wrist watch style device offers dual-band Bluetooth 5.0/ANT capability for easy connection to cycling computers and smartphone apps, plus USB rechargeable battery with up to 24-hour run-time. IPX7 rated to withstand the elements, the OHR-31 also features an LED low battery indicator and auto shutdown mode for maximized battery life. Multiple armband sizes included. Enjoy effortless tracking of your heart rate without the bulk of a chest strap.