This chest strap is lightweight and water resistant it also prevents that cross-talk from other heart rate and electrical devices for accurate measurement. At the core of your heart rate training is the Polar T31 coded?One-piece moulded?strap. Its job is a simple one: to transmit your heart rate data to your Polar wrist unit. The Super sleek and light weight ECG (electrocardiogram) can accurately communicate in water and has is designed for all weather condition. Key features Built to last with up to 2500 hours of training usage Coded to Prevents cross-talk from other electrical devices for accurate measurement of your training Transfers heart rate information while swimming?100% waterproof construction? The POLAR T31 coded transmitter belt was designed for reliability and durability.