This is the only monitor that audibly transmits your heart rate while swimming. Without the need to wear a telemetry strap or wrist watch, the 100% waterproof monitor's clip attaches to an ear lobe to detect pulse using infrared technology. The monitor clips to a swim goggle's strap and rests against either temple, using bone conduction to transmit sound to the wearer through the cheek bones to the inner ear. You can set the monitor to announce your heart rate anywhere from 5-, 10-, 20-, 30-, or 45-second to 1-, 2-, and 5-minute intervals during a swim workout (a heart rate of 142 is heard as "one forty two" in an easy-to-understand voice). The monitor remains secure to goggles even during the most vigorous swimming strokes. Its rechargeable battery provides up to eight hours of operation after charging via a computer using the included USB cable. 3 1/2" L x 1 1/2" H x 1/2" D. (1 oz.)