Heart rate monitors are fitness accessories designed to track how hard your heart is working when you exercise; this allows you to put enough stress on your heart to strengthen the muscle while minimizing the risk of overexertion. These devices come in a variety of makes and models, but most are comprised of two basic units: a transmitter and a wrist-mounted receiver. Both of these units require battery power to function properly; as such, it is important that you learn how to tell when one of the batteries requires replacing.
Moisten the electrodes located on the rear of the monitor's transmitter. Place the transmitter over the center of your chest, with the electrodes pressed against your skin. Wrap the transmitter's strap around your body and buckle the device into place.
Press the “mode” button on the watch unit and check the display to see if the device responds. If the display appears frozen, attempt to reset the device by holding down all of the buttons for five to 10 seconds. If the watch unit fails to respond, install a replacement battery in the device.
Press the watch unit's “mode” button until you have accessed the heart rate display. If the device fails to show an accurate reading, move to a different location, away from any potential sources of electrical interference, and try again.
Adjust the position of the transmitter on your chest and confirm that there is sufficient moisture on the electrodes. If you are still unable to get an accurate reading and the rest of the watch's features are functioning properly, install a replacement battery in the transmitter.
Insert a small coin into the slot on the battery cover. Use the coin to turn the cover until it comes free. Remove the cover and discard the dead battery.
Insert the replacement battery into the device's battery bay, according to the diagram printed inside the bay; if no diagram is present, install the battery with the positive terminal facing upward.
Replace the battery cover onto the battery bay. Use the small coin to turn the cover until it locks into place.