A pair of glasses with a heart-rate monitor according to one embodiment. The heart-rate monitor is configured to measure the heart rate of the user of the glasses. The heart-rate monitor can include a sensor with a radiation transmitter and a radiation receiver. The radiation could be infrared radiation. In one approach, the receiver measures signals transmitted by the transmitter through a body part of the user to measure the user's heart rate. The sensor could be incorporated in a clip to clip onto the body part of the user, such as the ear lobe of the user. In another approach, the receiver measures signals transmitted by the transmitter and reflected by a body part of the user to measure the user's heart rate.