Specifically designed for triathletes. Our smallest and lightest heart rate monitor (HRM). Comfortable, easily adjustable strap. Stores and forwards heart rate data to your compatible device. Compatible Devices: fenix 3 Sapphire and fenix 3 Sapphire HR, Descent Mk1, Edge 1000, Edge 1030, Edge 130, Edge 25, Edge 530, Edge 810, Edge 820, Edge 830, Fenix 3, fenix 5 series, fenix 6 series, forerunner 735XT, Forerunner 920XT, Forerunner 935, Forerunner 945, quatix 5, tactix Bravo, tactix Charlie, virb 360.