ESPHome detects when an LD2450 presence radar stops sending valid frames while the ESP device itself remains online. Live presence, target counts and positions become unknown instead of keeping the last reading indefinitely, and an optional connection sensor reports the loss.
The default timeout is five seconds. A powered, empty-room radar still sends frames, so an empty room does not look disconnected. The first valid frame restores the readings, while deliberate radar restarts receive a bounded grace period to avoid false alarms.