Computes and sends 6 running dynamics metrics to your compatible device. Battery life: replaceable battery lasts up to 1 year (assuming 1 hour daily use). Automatically turns itself on and off. Tiny size: at less than 0.5 ounces, you’ll forget it’s there. Compatible devices connect² with the Garmin Connect™ Mobile app to automatically sync your data and connect with others. Compatible Devices: Descent Mk1, fenix 5 series, fenix 5 Plus series, fenix 6 series, forerunner 245 and 245 Music series, Forerunner 645 and 645 Music series, Forerunner 935, Forerunner 945, Quantix 5, Tactix Charlie.