Shelly Flood S Gen4: The Compact Matter Leak Sensor

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TL;DR

Shelly's compact Flood S Gen4 puts Matter and Zigbee 3.0 in an IP67 leak sensor the size of a bottle cap. Here's what it does, what's new, and the specs Shelly hasn't confirmed yet.

Shelly quietly showed one of the more interesting leak sensors of the year at Light + Building in Frankfurt back in March 2026, and it almost slipped past everyone. The Shelly Flood S Gen4 is a tiny water sensor the size of a bottle cap that somehow crams in Matter, Zigbee 3.0, and Wi-Fi 6. For a device whose entire job is to sit on a floor and wait for a leak, that's a surprising amount of radio.

If you already run Shelly gear, our Shelly and Home Assistant integration guide covers how these devices behave on a local setup, and the Flood S slots into that same story. Let's break down what it actually is.

What Is the Shelly Flood S Gen4?

It's a compact, battery-powered water leak sensor. Shelly's knowledge base lists it as model S4SN-0071Z, and the spec sheet is the authoritative source here, not the marketing copy.

The short version:

Connectivity: Wi-Fi 6, Bluetooth 5 LE, Zigbee 3.0, and Matter over Wi-Fi. No Thread.
Detection: onboard stainless-steel triple-pad rather than a trailing cable.
Battery: one CR123A cell, rated around two years depending on use and network.
Rating: IP67, so it shrugs off dust and temporary submersion.
Size: roughly 23 by 77 mm, about 70 grams with the battery in.
Alarm: a built-in buzzer plus a light alarm, with three intensity profiles.

A couple of things Shelly has not published, so I won't invent them: there's no decibel figure for the alarm, and the spec page lists an operating temperature range rather than a dedicated room-temperature reporting sensor. If you need ambient temperature logging from this exact unit, wait for the shipping firmware to confirm it.

What's Actually New: Matter and Zigbee

Here's the part that matters. The older Shelly Flood puck was a Wi-Fi and Bluetooth device, full stop. No Zigbee, no Matter. The entire Gen4 flood line changes that by adding Zigbee 3.0 and Matter over Wi-Fi, which is a genuine generational jump rather than a spec bump.

Why does that matter for a leak sensor? Because leak sensors are exactly the kind of device you want to buy once and forget, and interoperability is what lets you forget it. A Matter sensor joins Apple Home, Google Home, Alexa, SmartThings, and Home Assistant without you praying it picks the right app. Zigbee gives you a battery-friendly fallback if you'd rather keep it off Wi-Fi. That's a smarter foundation than yet another cloud-locked puck.

The one asterisk, and I think it's a real one: no Thread. Plenty of 2026 Matter sensors lean on Thread for low-power mesh, and Shelly went Wi-Fi and Zigbee instead. Neither approach is wrong, but if your home runs on Thread border routers, know that going in.

S Gen4 vs the Regular Flood Gen4

This is where people will get tripped up, so let's be clear: there are two separate products with almost the same name.

The Shelly Flood Gen4 (no S) is the larger, cable-based unit. It shipped in November 2025 at $32.99, uses four AA batteries, carries an IP44 rating, and comes with a two-meter leak-sensor cable you can extend to run along a wall or under an appliance.

The Shelly Flood S Gen4 is the compact redesign. It drops to a single CR123A cell, jumps to IP67, ditches the cable for onboard pads, and shrinks dramatically. Think of the cable version as the one you snake behind a washing machine, and the S as the one you tuck under a sink and never see again. Same brains, different body.

Should You Wait for It?

Honestly? If you need leak protection today, the regular Flood Gen4 is already on sale and does the job. The Flood S is the one to wait for if you want the smallest possible sensor with the highest water rating, and you don't mind that Shelly hasn't confirmed a price or a firm shipping date yet.

I'd hold off on pre-ordering from any third party quoting a number, because that number isn't official. Watch shelly.com and the Matter certification listings (Matter Alpha covered the Matter-no-Thread detail), and buy once the price is real.

For a device this cheap and this quiet, the Gen4 line finally makes the boring water sensor a first-class Matter citizen. That's the update worth caring about, not the exact millimeter of the shell.

Frequently Asked Questions

Does the Shelly Flood S Gen4 need a hub?

No. It speaks Matter over Wi-Fi and Zigbee 3.0, so it can join Apple Home, Google Home, Amazon Alexa, SmartThings, or Home Assistant either directly over Matter or through a Zigbee coordinator you already run. You can also use it as a plain Wi-Fi device through the Shelly app. A separate Shelly hub is not required.

Does the Shelly Flood S Gen4 support Thread?

No. This is worth flagging because a lot of new Matter sensors use Thread for its low-power mesh. The Flood S Gen4 runs Matter over Wi-Fi instead, plus Zigbee 3.0 and Bluetooth 5 LE. If your setup leans on a Thread border router, this sensor won't join that mesh, it'll sit on Wi-Fi or Zigbee.

How much does the Shelly Flood S Gen4 cost?

Shelly had not published an official price or firm on-sale date at the time of writing. The sensor was shown at Light + Building in March 2026 and has a full spec page in Shelly's knowledge base, so it's close to launch, but any price you see quoted right now is a guess. For reference, the larger cable-based Shelly Flood Gen4 launched in November 2025 at $32.99, and the compact S usually lands near its sibling.

Will the Shelly Flood S Gen4 work with Home Assistant locally?

Yes. Shelly's Gen4 devices support local control, and Home Assistant talks to them through the native Shelly integration over the local RPC API, with MQTT available as well. Matter over Wi-Fi also allows local onboarding. Confirm MQTT behavior on the shipping unit if fully local, cloud-free operation is a hard requirement for you.