Sonostar SmartFit Activity Tracker Deluxe Kit - Medium Blue No charging required! Replaceable coin battery lasts up to six months Tracks steps, distance, calories burned; monitors and analyzes sleep duration and patterns Each Deluxe Kit includes one Smart Fit sensor with coin battery, 3 interchangeable color case inserts and 3 different size wristbands (S/M/L) in same color. Build a 'Family Network' by inviting other Smart Fit users to join and compare daily activities Works with the free mobile app available at Google play and iPhone App Store; for use with iPhone 4S and later or Android 4.3 and later