A motorised 1-inch shutoff valve with a flow meter in the same body, speaking Z-Wave Plus with S2. Home Assistant can include it directly in Z-Wave JS, which puts whole-home water shutoff and consumption data on the mains without an Alarm.com account.
This is a plumbing job, not an electrical one. The valve is 1-inch male NPT at both ends and needs fittings to match whatever the incoming main actually is, so it goes in with the water off and a plumber on site. The control unit runs on 100-240VAC, which means a socket or a fused spur within reach of the stop tap rather than a battery to change.
Being mains powered and permanently listening, it also repeats, so a valve on the incoming main often turns out to be the Z-Wave node that finally links the plant room to the rest of the mesh.
What makes it worth the trouble is the meter. It watches flow rate and duration rather than waiting for a puddle, so a continuously running toilet or a slow joint shows up as a pattern the house does not usually have, and a burst closes the valve on its own. Z-Wave JS exposes the high, medium, and low flow thresholds and timers as configuration parameters, along with whether each one closes the valve, sounds the buzzer, or only reports, so the thresholds are tuned in Home Assistant rather than in the Alarm.com app.
Note that Z-Wave JS’s parameter definitions for this device were reverse engineered from Zniffer traces rather than published by the manufacturer, so verify behaviour against the valve before trusting a threshold to close the mains unattended. Pair it with leak sensors at the usual failure points and treat the meter as the second line, not the only one.
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