Paid promotion for Shelly. Illustrative story.
The inlet hose on our dishwasher is about forty centimetres long. Rubber, with a metal braid, a clip at each end. It cost eleven euros when the machine was new.
On a Tuesday in March, at some point after we left for work, the clip on the machine end let go. The machine was not running. It did not need to be. The hose is under mains pressure whether the machine is on or not.
We came home at ten past six. The water had been running for nine hours.
This is what nine hours looks like, what it cost, and what is under the sink now.
The inlet hose on our dishwasher is about forty centimetres long. Rubber, with a metal braid, a clip at each end. It cost eleven euros when the machine was new.
On a Tuesday in March, at some point after we left for work, the clip on the machine end let go. The machine was not running. It did not need to be. The hose is under mains pressure whether the machine is on or not.
We came home at ten past six. The water had been running for nine hours.
This is what nine hours looks like, what it cost, and what is under the sink now.
The inlet hose on our dishwasher is about forty centimetres long. Rubber, with a metal braid, a clip at each end. It cost eleven euros when the machine was new.
On a Tuesday in March, at some point after we left for work, the clip on the machine end let go. The machine was not running. It did not need to be. The hose is under mains pressure whether the machine is on or not.
We came home at ten past six. The water had been running for nine hours.
This is what nine hours looks like, what it cost, and what is under the sink now.
The kitchen is on the first floor. The floor is engineered oak on a chipboard sub-floor. Below the kitchen is our neighbour's bedroom.
By six in the evening the water had crossed the kitchen, gone under the wall into the hall, and come through the ceiling downstairs in two places. The oak was already lifting. The chipboard under it had swollen to the point that the dishwasher was sitting on a slope.

Nobody looks behind a dishwasher. That is not carelessness. It is where dishwashers go.
Then the things nobody claims for. The drying machines ran for 26 days. Two of them, one downstairs. They are not quiet and they are not cheap to run. Our electricity bill for that month was 94 euros higher than the one before.

A friend who does home automation for a living came round about a week after. He did not say much. He put a flat white sensor on the floor of the cupboard under the sink, ran a braided cable from it along the dishwasher hose and behind the washing machine, and stuck a small square thing to the wall inside the cupboard.
Then he poured a glass of water on the cable. My phone buzzed before the glass was empty. The sensor under the sink was sounding at the same time.
The test. Twenty-nine seconds from the glass of water to the all clear. In March the same event took nine hours.
This is the kit he put in. It is 72.60 euros as a set.
The answer to that is a valve on the main supply that closes when a sensor gets wet. It is about 117 euros and it goes after the stopcock, so a plumber fits it. It is the next thing on the list. The sensors were the first thing because without them the valve has nothing to listen to.
Sensors are the alarm. The valve is the hand on the tap. You need the first one before the second one is any use.
What it would have cost against what it cost
A floor sensor for under the sink, a length of sensing cable for the hose run behind the washing machine, and a humidity sensor for the wall that gets damp before it gets wet. The cable bracket comes with it. 72.60 EUR against 82.50 bought separately.
Pick the colour of the humidity sensor above. The shut-off valve is offered on the next page, for when you want the water stopped, not just reported.

"Working wery well. I had some water on the floor and it imidiently started beeping."

"Reactivity in the shelly app not so perfect Good via MQTT through a domotic box"
Four stars and below are left in. The cable has the weakest score of the three on the store, and the complaint is the plug where it meets the sensor. Push it home until it clicks and clip the cable so nothing pulls on it. That is what the brackets in the kit are for.