A few drops, and my phone speaks up
A leak sensor under 20 euros passed a real water test in my Vienna flat: instant alert, all-clear after 30 seconds, battery warning included.
If you automate exactly one thing, make it this: put a leak sensor next to the washing machine. The device costs less than a box of detergent, takes twenty minutes to set up, and the damage it prevents runs into the thousands. Nothing else in my setup has such a lopsided ratio between effort and possible benefit.
I actually tested the sensor in Vienna with water, not just configured it. Here is what happened.
The test
Sensor on a flat surface, a few tablespoons of water poured over it. The two contacts on the underside close as soon as something conductive bridges them — there is no more physics to it than that.
The test ran on 28 August 2026. The log records the edges to the second: triggered at 12:07:22, dry again at 12:07:31. Both edges arrived — and that is the real checkpoint, because a sensor that only reports the trigger leaves you in the dark.
What happens:
- Alert as a critical notification. Not an ordinary push but a critical alert, which breaks through silent mode and Focus. That is exactly what the category is for: not parcel announcements, but the thing that is allowed to wake you at three in the morning.
- A notification that stays. A persistent notice also lands in Home Assistant, with a timestamp. It does not disappear on its own.
- All-clear after 30 seconds. Once the contact is dry, a waiting period runs and a second notification follows — silent, because it does not need to wake anyone.
- Battery warning. Two triggers: the sensor’s own low-battery report and a threshold at 20 per cent. A sensor that quietly runs flat is worse than no sensor at all — it lulls you into thinking you are covered.
The sentence that matters
The all-clear does not say “everything is fine”. It says: The sensor has reported dry for 30 seconds. Worth a look anyway.
And the persistent notice in Home Assistant deliberately stays, even after the all-clear. The reasoning, straight from the configuration: being dry again does not mean nobody has to look. A sensor that clears after nine seconds may have seen water for exactly nine seconds — and that water went somewhere.
What I run
| Component | In use here |
|---|---|
| Sensor | Zigbee leak sensor |
| Radio | Zigbee via Zigbee2MQTT |
| Coordinator | Sonoff stick |
| Hub | Home Assistant |
| Notification | Push to iPhone |
One thing for context: the sensor sits at the washing machine. That is the spot most likely to leak in my flat, and it is the spot I tested.
What this setup cannot do
This is where a lot of videos get sloppy, so to be explicit:
- It does not close a valve. My setup reports, it does not intervene. A motorised shut-off valve is a separate project with its own effort, and it belongs on the main line, not on a hose.
- It does not replace looking. If you are away for three days you get a notification — not a towel.
- It only protects the spot it lies on. A sensor under the washing machine tells you nothing about the sink, the boiler or the heating system.
Where a sensor genuinely pays off
After running this in three homes there is a clear order. The top entry is what I would cover first:
- Washing machine and dishwasher — hose, seal, pump: the most things that can fail, and it happens while the machine runs.
- Boiler or hot water tank — rarely leaks, but goes unnoticed for a long time when it does.
- Heating manifold — above all in a house nobody checks regularly.
- Under the sink — often the first place people think of, but usually the one you notice early anyway.
More than one sensor per spot adds nothing. Four spots with one sensor each beats two sensors on the same machine.
Deliberately no siren
There are two sirens in the house. They stay out of this, and that is a decision, not a gap.
Water escaping at the washing machine is damage, not a break-in. A siren going off helps nobody while you are away — there is nobody there who could act — and while you are home it startles you when a notification would have done. Noise is only the right answer when somebody should run away or be driven off. Neither applies to water.
If you see it differently, wire the siren into the same automation. The point is not that it would be wrong — the point is to decide it rather than let it tag along.
So what?
A leak sensor is not a smart home project, it is insurance with a one-off cost. If you are starting with Home Assistant and do not know where to begin: begin here. The test takes five minutes, you see the result immediately, and you end up with an automation that prevents something real instead of just dimming lights.
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