Heart rate in and out of the water most heart rate monitors do not work under water the poolmatehr has been specially designed for swimmers so it will transmit when in the pool view your heart rate on the watch during your swim and download afterwards for further analysis you can also use it as a heart rate monitor out of the pool for other activities the majority of modern heart rate monitors operate at 24ghz which does not penetrate water so they will not show heart rate in the pool the