Heart Rate Monitor HR-100C... Knowing your heart rate is important because if you are working out too hard, your activity can become counter productive and strain muscles. To achieve an effective workout, no matter what the aerobic activity, you must maintain your heart rate at a proper level for a minimum of 20 minutes. The proper level is generally 65%-85% of your maximum heart rate. FEATURES: Easy to program monitor with ventilated watch band; Backlight function; Alarm option for low and high heart rates; Mounting bracket to mount watch receiver to most treadmills and bicycles; Soft zippered storage case; Water resistant watch and chest transmitter belt to 98 feet (30 meters); Time of day display and daily reminder alarm feature; Includes chest belt.