When someone’s phone sits on a table or sofa up to three feet away, the app can monitor their breathing and movement. The app isn’t yet publicly available, but it will likely alert users when it detects a problem, and if it doesn’t get a response, automatically dial 911. It uses sound waves to work: The smartphone speaker emits inaudible sound signals, which bounce off someone’s chest as they breathe. The phone’s microphone records the echoes of that sound, and using that data, an algorithm can monitor someone’s breathing and note when it slows or stops. The app can also monitor movement and register when someone becomes motionless.