SUPREME ACCURACY & SIZE GUIDE: Polar H10 delivers precise ECG/EKG heart rate tracking trusted by pro athletes. Sizes: XS–S 62–74 cm, M–XXL 75–115 cm, XXXL 116–155 cm (sold separately). Between sizes : M–XXL for comfort, XS–S for tighter fit. CONNECTIVITY: Connect via Bluetooth, ANT+, or 5 kHz to smartwatches, fitness apps (Peloton, Strava, Nike), or gym equipment. Supports dual Bluetooth and ANT+ connections. POLAR PRO CHEST STRAP: Improved electrodes, non-slip silicone dots, and a secure buckle ensure a comfortable, accurate, interference-free fit. Replace strap approx. every 6 months for best performance. VERSATILITY: Ideal for cycling, running, swimming, rowing, and gym workouts. Waterproof up to 30 m with internal memory for one training session without a phone or watch. COMPATIBILITY: Works with Polar, Garmin, Apple Watch, Suunto, and many apps. Update firmware easily via the Polar Beat app.