Parents could watch their baby’s heart rate from another room without using any kind of wearable device or special sleeping pad with a new development out of MIT that uses Wi-Fi signals to track the rise and fall of peoples’ chests.

Researchers at the Computer Science and Artificial Intelligence Laboratory transmitted a low-power wireless signal through a wall and measured how long it took the signals to bounce back. Changes in the reflected signals allowed the team to measure movement, or even minute chest movements.

Based on a person’s chest rising and falling, the CSAIL group can determine their heart rate with 99 percent accuracy. The system can track up to four people at a time.

“It has traditionally been very difficult to capture such minute motions that occur at the rate of mere millimeters per second,” paper co-author Dina Katabi said in a release. “Being able to do so with…