If you have ever set up a smart home device or complained about a dead zone in your living room, you know how crucial Wi-Fi is to modern life. But beyond streaming high-definition video or connecting your smart thermostat, your humble Wi-Fi router is quietly developing a surprising new capability: it can act as a highly sensitive, contactless health monitor.

No smartwatches. No chest straps. No intrusive cameras recording you while you sleep. By reading the tiny disruptions in the wireless signals already blanketing your home, researchers can measure your breathing rate, detect sleep apnea, and spot falls from across the room.