Empty-Home Water Sentinel

Water changes how WiFi passes through a wall far more than almost anything else. As a leak spreads, signals crossing that wall slow down and weaken in one spot that keeps growing. The change stays in one place and only grows — nothing else in an empty house behaves like that.

In the physics: Water has eps_r~80 vs ~2 for dry drywall/wood; even a few percent moisture gain in a wall cavity measurably increases dielectric constant and loss along paths traversing it — shortening apparent electrical delay, attenuating specific CIR taps, and shifting the reconstructed eps_r field in that voxel. The change is spatially localized and monotonic, unlike occupancy clutter.