In-Wall Pipe Leak Early Warning

Water escaping a pressurized pipe makes the pipe and the wall around it tremble faintly, and that trembling shakes the signal. At the same time, the escaping water slowly changes how signal passes through that wall section. A steady hiss plus a growing wet spot in the same place is almost certainly a leak — and almost nothing else.

In the physics: Turbulent outflow at a leak orifice makes the pipe and surrounding wall vibrate at 5-40 Hz (within CSI micro-Doppler band), phase-modulating paths that graze the pipe run; simultaneously the escaping water raises eps_r locally, drifting the delay of paths through that wall section. The AND of a persistent narrowband vibration line plus a co-located slow dielectric drift is nearly unique to a leak.