What we like
- Included 2 m cable detects water along its whole length
- Additional sensing cable costs €7.90 per 2 m
- Built-in buzzer and four replaceable AA batteries
What could be better
- Cable contact with conductive metal or condensation can cause false alarms
- Bulkier and €16 more expensive than the Flood S Gen4
- Five-second sensing interval; Economic mode silences the buzzer
The cable is the reason to buy it
Flood Gen4 solves a weakness of a small leak-detection puck: water may run past the spot where you put it. Shelly includes a two-metre sensing cable that detects water anywhere along its length. Running that cable beside an appliance or along a cabinet base gives a leak more opportunity to reach the sensor. It still only detects water that touches the cable; it does not monitor an entire room from the wall.
The EU shop had it in stock at €34.90 including VAT on September 9, 2026, with shipping extra. Another two metres of sensing cable costs €7.90, making a four-metre arrangement €42.80 before shipping or extra mounting clips. Shelly supports extensions up to 150 metres, though that upper limit is a specification, not a distance we have tested.
That expandable coverage is a worthwhile distinction. Buying it merely to sit under one pipe wastes much of the advantage over the smaller Flood S.
More flexible placement, more hardware to hide
The 97 × 76 × 25 mm white main unit is a small wall-mounted box, with four replaceable AA batteries included. It is more conspicuous than a floor puck, and the cable needs a sensible route. In return, the main unit can stay accessible above the floor while the sensing cable reaches the leak-risk area.
The enclosure is rated IP44. Keep the main unit out of floodwater; the cable is the part intended to detect the leak. Shelly also identifies two sources of false alarms: the sensing cable touching conductive metal, and condensation in humid surroundings. A cable draped over a pipe or metal rail is therefore a poor match for this design.
Those physical constraints matter more than the range of smart-home logos. The cable is useful when you can position it deliberately, less appealing when there is nowhere suitable to secure it.
An audible alarm with some easily missed limits
The built-in buzzer gives you an alert at the device as well as the option of connected notifications. In the default Normal profile, the initial alarm pattern runs for five minutes, then repeats for one minute every half hour while the flood state persists. Intense repeats more often. Economic disables the buzzer, including its low-battery warning; Rain mode reports the water state without a flood alarm.
Despite the marketing language, detection is not instantaneous. The sensor checks for water every five seconds. A configurable state-hold delay can filter brief changes, but adds waiting time before the state changes. Neither a more persistent buzzer nor the Matter badge guarantees immediate delivery to a phone.
Matter over Wi-Fi is included, with Zigbee available through alternative firmware. For automatic water shutoff, a separate compatible valve and automation are required; this sensor cannot close a pipe itself.
Pay for a longer detection area
Choose Flood Gen4 for a useful cable route around a washing machine, beneath cabinets or beside plumbing. For a single spot where water is likely to collect, Flood S Gen4 saves €16 and removes the cable clutter. Two Flood S units cost €37.80 and can watch separate locations, while this model's cable is the better fit for one continuous area.
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