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A white Shelly Flood Gen4 on a laundry wall, with its leak sensor cable running along the floor beside a front-loading washing machine and through a puddle of water

Know the moment there's a water leak

How it works

The Shelly Flood Gen4 goes on the wall beside the appliance or pipe you're worried about, with its leak sensor cable along the floor. The cable comes in the box and picks up water anywhere along its length, so one sensor can cover the floor behind a washing machine or around a hot water unit.

It runs on batteries and joins your Wi-Fi directly, so there's no hub to buy. It checks for water every 5 seconds. When it finds some, two alarms go off: the sensor's own buzzer, for anyone at home, and an alert on your phone that sounds even if you're out. You don't need to set up a rule for this: the alert comes with the sensor.

  1. Flood Gen4 01

    Shelly leak sensor

    Sits on the floor and checks for water every 5 seconds.

  2. 02

    Water reaches it

    The buzzer sounds straight away, so anyone home hears it.

  3. iPhone lock screen showing a critical Shelly alert that water was detected by a sensor named Laundry leak sensor. 03

    Your phone

    Sounds an alert naming the sensor, wherever you are.

What it looks like on your phone

  • Straight to your phone. The alert names the sensor, so you know it's the laundry.

  • Flood, at a glance. The sensor's screen turns red while it's wet and goes back once it's dry.

  • One alert per sensor. A second sensor under the sink sends its own, by name.

Step by step

  1. Pull the battery tab

    The batteries are already in. Pull out the paper tab that keeps them from connecting, and the sensor switches on. On the Flood Gen4, plug the leak sensor cable into the sensor as well.

  2. Add it over Bluetooth

    In the Shelly Smart Control app, tap the plus sign, choose Add via Bluetooth and tap Next.

  3. Pick the sensor

    The sensor shows up in the Bluetooth scan as soon as its tab is out. If it doesn't, press its button once. Pick it, choose your Wi-Fi network, then a room, and name it after where it'll sit, such as Laundry leak sensor.

    Learn how to add a device to the Shelly app

  4. Choose how loud it is

    Open the sensor, go to Sensor settings and then Alarm mode. Leave Flood mode on and pick Normal, which sounds the buzzer until you press the sensor's button. Intense sounds more often, and Economic sends the alert without the buzzer. Tap Save.

  5. Put it where the water would go

    Mount the Flood Gen4 on the wall beside the appliance and lay the cable flat along the floor where a leak would run, behind the washing machine or around the base of the hot water unit. The Flood S Gen4 sits flat on the floor, pads down, under the sink trap or in the drip tray.

  6. Test it

    Touch the cable or the pads with a damp cloth. The sensor's buzzer starts and your phone sounds an alert within a few seconds. Dry the sensor, and press its button once if the buzzer is still going.

Frequently asked questions

Should I use the Shelly app or Home Assistant?

If you don't run Home Assistant, use the Shelly app: the alert comes with the sensor, with no rule to set up. If Home Assistant already runs your home, add the sensor there, so the leak can set off your other automations too.

Will I hear the alert if my phone is on silent?

On iPhone, Shelly sends the flood alarm as a critical alert, which sounds with the phone on silent as long as critical alerts are allowed for the Shelly app under Settings, Notifications.

Which sensor should I get?

The Flood Gen4 suits anywhere a leak could spread along the floor, like behind a washing machine, because its cable covers a strip rather than a spot. The Flood S Gen4 is smaller, with no cable, for one spot such as under a sink trap or in a drip tray, and it's rated IP67.

How long do the batteries last?

About two years, according to Shelly, depending on the batteries and your Wi-Fi signal. The app shows the battery level, and the sensor gives a short beep when it drops below 20%.

What do I do after an alarm?

Fix the leak, then dry the sensor or its cable with a cloth. It reports dry again by itself, and you can reuse it straight away.

Can I watch more than one spot?

Yes. Add a sensor for each place, such as the laundry, under the kitchen sink and beside the hot water unit, and name each one after where it sits. The alert names the sensor, so you know where to look.

Do I need a hub?

No. The sensor joins your home Wi-Fi directly and alerts come through the Shelly app. It also speaks Zigbee and Matter if you'd rather add it to a smart home system, but you don't need either for the alerts.

What if the internet drops out?

The buzzer still sounds, because the sensor makes that call itself. The phone alert needs your Wi-Fi and the internet to get through.

Will I get two alerts?

If the sensor is still in your Shelly account, the Shelly app sends its own alert as well as Home Assistant's. Turn off notifications for the Shelly app on your phone if you only want one.

What about Android?

The automation works the same way. On Android, Home Assistant's notification channels decide whether the alert sounds with the phone on silent; the companion app's documentation on critical notifications covers it.

Do I need the internet?

The sensor and the automation work over your home network, and the buzzer sounds whatever happens. The alert reaches your phone through Apple's or Google's push service, so that part needs the internet.

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