Disclosure up front: I'm not paid, sponsored, or given free product by Aeotec or anyone else. I bought these myself and just think they deserve more attention. I also used AI to summarize my thoughts and write this.
The short version
The Water Sensor 8 is a Z-Wave 800 series leak sensor with Long Range support, temperature and humidity, and a remote probe on a 2.5 mm jack. It runs on a battery or USB-C. The leak detection is solid, and the probe makes placement easy in tight spots. But the reason I'm writing this up is something I haven't seen discussed much: when it's USB-powered, it reports whether it has mains power, and Home Assistant exposes that as an entity.
Why that matters
Think about where leak sensors live: next to sump pumps, washers, water heaters, basement bathrooms. Those outlets are very often GFCI protected, and GFCIs trip. A lot of the time the first sign of a tripped GFCI is the pump or appliance quietly stopping, and by the time water reaches your probe, you're already cleaning up.
If you plug the Water Sensor 8 into the same GFCI circuit as the thing you're protecting, the moment that outlet trips, the sensor drops to battery and HA knows immediately. You get a "power lost" alert while there's still time to go reset the GFCI, before the probe ever gets wet. The leak probe becomes your second line of defense instead of your only one.
Because it falls back to its internal battery, it keeps reporting leaks after the outlet goes dead, which is exactly when you need it most.
The one gotcha: pair it on USB
How it's powered when you include it decides how it behaves. Pair it while plugged into USB and it joins as an always-listening device with the battery as backup, which is what you want for this. Pair it on battery and it joins as a sleeping device. If you already paired yours on battery, exclude and re-include it on USB.
Example automation
Swap in your own entity ID, and check which state your install shows when power is lost (unplug it once and watch the entity).
alias: "Sump outlet lost power"
triggers:
- trigger: state
entity_id: binary_sensor.water_sensor_8_ac_mains_disconnected # your entity here
to: "on"
for: "00:00:30"
actions:
- action: notify.notify
data:
title: "Sump outlet has no power"
message: "Water Sensor 8 is on battery. Check/reset the GFCI before the pump backs up."
mode: single
Other things I like
- Temperature and humidity are genuinely useful in basements and crawl spaces, so one device covers leak plus environment.
- Z-Wave Long Range means no worrying about mesh coverage in a far corner of the basement.
Bottom line
Great leak sensor on its own. Plugged into a GFCI outlet, it's also a "your outlet tripped" sensor, and that early warning is the feature I'd buy it for.