The CELF™ wearable sensor generates medical-grade ECG measurement and thus superbly-accurate heart rate, in contrast to simple and often inaccurate pulse monitoring as used by widely established brands such as Fitbit® and Apple®. CELF's technology seamlessly measures and displays key cardiovascular data in real time to let users determine and train in their Dynamic Training Zone™. With CELF, the guess work is removed and the automation of one's real-time, ultra-accurate readings begins. Train for weight loss, cardiovascular conditioning, multiple sports (including swimming), or even Mindfulness. It’s safe, accurate, and passive. Additional sought-after features include body hydration monitoring, skin temperature, and respiration. The CELF sensor integrates instantly with many existing watch and device platforms as an “aftermarket” product; there is NO need to purchase a new watch or other interfacing device. CELF talks to all leading smartphone/watch/tablet platforms using state-of-the-art BLE 4.0 (Bluetooth Low Energy Technology). It's both wireless and fleaweight, and once contact is made with the skin, monitoring initiates continuously and passively. In typical athletic use, one battery charge will power your CELF sensor for up to 2 days, and recharging is a breeze using a standard micro-USB charger.