The transmitter of this heart rate monitor snaps into a pocket on a customized shirt to allow complete comfort and freedom of movement during exercise, unlike bulky chest straps that inhibit movement. The stretchable fabric sensors built into the shirt detect your heartbeat and hold the transmitter firmly against the body to produce consistent readings without the chafing and slipping common to straps. The fibers also wick away moisture to keep you dry during exercise. The wrist monitor automatically calculates target pulse ranges for walking, jogging or running or allows you to enter your own values and sounds an alarm or vibrates when your heart rate falls outside the range. It a lso computes calories burned. A tap on the backlit LCD display shows one of six readings (current heart rate, percentage of maximum heart rate, average heart rate, calories burned, stopwatch and clock) so you can track your progress during workouts without fumbling with buttons. The transmitter is easily removed for machine washing of the garment. Transmitter and monitor each require one CR2032 battery (included). Mens Sleeveless Top. Charcoal. Specify M (36-38), L (38-41) or XL (41-44).