Shelly Flood S Gen4

A useful small purchase for an unglamorous job

At €18.90, Flood S Gen4 is the easier Shelly leak sensor to justify for a single sink cabinet or appliance tray. It was in stock in Shelly's EU shop on September 9, 2026, including VAT with shipping extra. Two cost €37.80, which makes separate sensors in separate rooms a reasonable option.

The white round body is low enough to tuck into many spaces beneath appliances, without an external cable to route. Three groups of stainless-steel pads cover parts of its underside. Shelly designed the larger contact area for detecting water, including clean water with low conductivity; we have not tested its sensitivity or the smallest leak it can catch.

The placement tradeoff is straightforward. A puddle has to reach those pads. Water running along the other side of a cabinet can go undetected, so buying a sensor is only useful when there is a plausible path for water to reach it.

A replaceable battery in a sealed body

The IP67 enclosure is a welcome choice for a device that sits where water may collect. One CR123A battery is included and can be replaced, so a flat battery does not retire the sensor. Shelly estimates approximately two years of life, depending on use, the battery and connection strength. That is an estimate, not a measured result from us.

CR123A is less common in a household drawer than AA or AAA. Replacement also involves opening the enclosure and correctly reseating its seal, rather than simply sliding out a battery tray. Neither is a major objection at this price, but both belong in the ownership cost of placing several sensors around a home.

The buzzer makes it useful beyond the app

An audible alarm at the sensor is a practical extra when you are nearby. The default Normal profile sounds an alarm pattern for five minutes, then repeats for one minute every half hour while wet. Intense makes that reminder more persistent. Economic mode switches the buzzer off and also removes its low-battery chirp. Rain mode changes water reporting into a state without the flood alarm.

The sensor checks for water every five seconds. That is more specific than the shop's promise of instant alerts, and remote notification delivery adds a separate dependency on your network and chosen platform. Matter over Wi-Fi is included; Zigbee is an alternative firmware choice. Neither connection makes this a self-contained water shutoff system.

These choices make Flood S flexible, but they also mean the alarm profile matters. Someone buying it primarily for an audible warning should not choose the silent profile simply because its name sounds economical.

Spend more only when the cable helps

The €34.90 Flood Gen4 includes a two-metre sensing cable that detects water along its length. It is worth the extra €16 when the likely leak route extends along cabinets or around an appliance. Its larger wall-mounted box and four AA batteries are the physical tradeoff.

For one collection point, Flood S is the cleaner purchase: lower price, less hardware and an alarm at the spot you want to watch. For two separate locations, two pucks offer more useful coverage than trying to stretch one sensor between them.