The Mio LINK Heart Rate Wrist Band features Mio Continuous Technology with EKG-accurate heart rate data at performance speeds. This product has no chest strap, so you can train with heart in comfort.How Mio Heart Rate Technology works: LED lights and an electro-optical cell ?sense? the volume of blood under the skin. From there, sophisticated algorithms are applied to the pulse signal so that the heart?s true rhythm can be detected, even while cycling or running at performance speeds.Wireless Connectivity: Connect to your favourite mobile fitness apps through Bluetooth Smart (4.0) and ANT+ technology.Built for performance: During extensive testing against the top heart rate chest strap brands, Mio LINK consistently performed with 99% EKG accuracy, even while running at speeds of up to 14.4 mph.Stay in the zone and on track: Heart rate training is proven to help you train more efficiently and effectively, so you can optimize your performance and maximize your workout. Mio LINK offers up to 5 customizable heart rate zones with LED lights that can tell you which zone you?re in at any given moment, so you can stay on track with your training goals.Comfort. Form. Function: Mio LINK delivers maximum performance in ultimate comfort. Its soft, durable silicon strap ensures a snug and comfortable fit ? and with no need for a chest strap, you?ll be more comfortable than ever.Features:*Water resistant up to 30m depths*Customize your workout with up to 5 user-settable heart rate zones*Connect to your favourite fitness apps & sport devices with Bluetooth Smart (4.0) and ANT+. Check device compatibility*Designed for small - medium wrists (121-175mm / 4.8?-6.9?) *Water resistant up to 30m depths