Are you serious about your sport. If so you need a serious heart rate monitor.Mio Alpha is the worlds first strapless, continuous heart rate monitorthat is as accurate as a chest strap, even at performance speeds.Totally unobtrusive, Alpha delivers maximum performance in ultimatecomfort. With no chest strap you won't have to worry about it sliding down or chafing.Alphas soft, stretchable silicone wrist band ensures a snug fit in a formfactor that wont slow you down. So comfortable, you can wear it all day!Alpha is a true scientific breakthrough. Technology proven accurate in medical use, is now robust enough for sport. Sophisticatedalgorithms are applied to the pulse signal so that the hearts true rhythmcan be detected even while running at performance speeds. Features: Continuous heart rate display User-settable heart rate zones with visual and audible alerts Data review (total exercise time, average heart rate, time in zone) Activity timer Clock Connects to compatible smartphones usingBluetooth Smart technology Silicone soft strap with secure snaplatching system Negative dot-matrix LCD Tri-color LED heart rate zones USB charging dock with magneticalignment Rechargeable lithium battery Glossary: Connect to smartphones Using Bluetooth Smart technology, Alpha can connect with compatiblesmartphones, including iPhone 4s and newer. Take advantage of a widerange of great fitness apps, including: Endomondo, Wahoo Fitness, Map My Ride, Run Keeper, Map My Run, Strava Adidas mi, iBike Sports.