Time to throw out the Fitbit or AppleWatch: a new device promises to monitor your vital signs using a wireless signal broadcast through your house.

The system could be used to check on the health of sleeping babies, elderly parents, or even divine your mood during the season finale of your favorite show.

The device uses a low-power Wi-Fi signal like a radar beam and bounces it off people in the house. Called Vital-Radio, it senses each person’s digital signature separately.

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To check breathing rate, the signal looks at the rise and fall of a person’s chest cavity. When she exhales, the chest contracts and moves away from the antenna, so that the distance between the chest and the antenna increases, causing an increase in the reflection time. At full inhale, the chest is bigger and the distance is smaller.

By measuring the difference in distances, the Vital-Radio figures out the respiration rate and could tell if a person is sleeping, awake or highly agitated. To measure heart rate, the same signal detects tiny skin vibrations that can also indicate mood and stress levels.

The researchers boast that Vital Radio is greater than 99 percent accurate and can check vitals of several people at the same time.

“We are very excited about applications in health care, even in smart environments to monitor your health,” said Fadel Adib, a graduate student at the Massachusetts Institute of Technology’s Computer Science and Artificial Intelligence Laboratory and lead author of the new study. “If you have it in your home, you can ask does my baby breathe okay during sleep? It could also adapt the lighting and music in the home based on your mood.”

The key to making the technology work is using a signal that can detect minute movements of the human body, explained Dina Katabi, professor of electrical engineering and computer science at MIT, and an author on the study which was presented at the CHI2015 conference this week.

“The reflection or the movement is very soft and easy to miss,” Katabi said. “You have to have a refined algorithm to capture it. This is what will make it or break it for this device.”

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During testing, the Vital-Radio was able to distinguish between two different people, and people and dogs, for example. But it didn’t work as well if the person was sitting behind a laptop, Katabi said.

The wireless vital signs device could replace irritating and annoying sensors for hospital patients with certain kinds of skin problems, according to Kevin Fu, associate professor of EECS at the University of Michigan.

“You don’t want to put adhesives on a burn patient,” Fu said.

At the same time, the researchers will probably have to address security and privacy concerns about broadcasting of personal medical data, Fu noted. Wearable sensors are tougher to hack, but Wi-Fi less so.

All in all “it’s a pretty clever paper,” Fu said. “What’s impressive is they actually built it. That is happening less and less in academia these days and so it’s good to have a real demonstration and real systems.”