Ditch the chest strap and get accurate heart rate on your wrist Mio Continuous Technology with EKG-accurate heart rate data at performance speeds No uncomfortable chest strap, so you can train with heart in comfort Customize your workout with up to 5 user-settable heart rate zones Connect to your favorite fitness apps & sport devices with Bluetooth Smart (4.0) and ANT+. Check device compatibility Comes in two sizes (wrist sizes: S/M - 121-175mm / 4.8-6.9, L: 149-208mm / 5.9-8.2) View Sizing Chart Water resistant up to 30m depths Mio LINK Regular (S/M) Strap: 121-175mm / 4.8-6.9 Mio LINK Long (L) Strap: 149-208mm / 5.9-8.2 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 hearts true rhythm can be detected, even while running at performance speeds. Have we mentioned our technology is award winning? Wireless Connectivity Connect to your favorite mobile fitness apps through Bluetooth® Smart (4.0) and ANT+ technology. Check device compatibility 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 & 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 youre 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, youll be more comfortable than ever.