Wiktionary
heart rate monitor
n. A wearable device that allows a user to measure their heart rate in real time, usually consisting of a chest strap transmitter and a wrist receiver.
Wikipedia
Heart rate monitor
This article refers to a device used by non-scientists. For the article on the medical device performing a similar function, see Electrocardiography.
A heart rate monitor is a personal monitoring device that allows one to measure one's heart rate in real time or record the heart rate for later study. It is largely used by performers of various types of physical exercise.
Usage examples of "heart rate monitor".
He screamed when his heart rate monitor beeped at him the first time.