The system, called Vital-Radio, works in a way very similar to radar. The Wi-Fi router puts out a signal that bounces off all of the people and objects in the vicinity. Based on how quickly the signal comes back, the system uses an algorithm to distinguish between an inanimate object and a person, as well as distinguishing between people and their individual body parts. It can track breathing through the tiny movements as a chest rises and falls, and the pulsating movements of the neck as our heart beats indicate the heart rate. However, the system is not perfect; Vital-Radio can’t pick up such minute physical changes when someone is walking, but at home or in a hospital when a person is mostly sedentary, it’s quite accurate, as the researchers found when they tried the system on 14 test subjects outfitted with heart and breathing monitoring devices for comparison.