EUC Garmin Running Dynamics Pod, measures Advanced Running Metrics. maybe used for a few runs, hasn't used it in a few years so battery should still be fine but can be replaced includes box with instructions and device. info from website: Computes and Transmits Meaningful Data Computes and sends 6 running dynamics metrics to your compatible device¹ 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