Water damage is one of those expensive surprises that happens when you’re not looking. The Honeywell RWD21 Water Leak Alarm is a simple fix for that blind spot. It sits on the floor and detects water as shallow as 1/16 of an inch—about the thickness of a nickel. Place it near a water heater, under a sink, or behind a washing machine. When moisture touches the sensor, it fires off an 85-decibel alarm. That’s loud enough to hear from another room, even over a running dishwasher.

The setup takes seconds. Pop in one 9V alkaline battery, set the unit on the lowest point of the area you’re monitoring, and you’re done. No Wi-Fi, no app, no subscription. That simplicity is the point. The alarm runs on a remote control method, meaning it’s self-contained and reliable without depending on your home network. It’s ideal for spots you check once a year or less, like sump pump pits or behind a refrigerator’s ice maker.

One honest note: this is a local alarm only. If you’re away from home, you won’t get a notification. For that, you’d need a smart sensor with push alerts. But for catching a slow leak before it rots a cabinet or warps a floor, the Honeywell does its job without fuss or false alarms.