I bought these for a "rainy day" and didnt expect to actually need them. Turned out, these tiny alarms saved my house, twice! There are three in the package, so I placed one behind my washing machine, one under the kitchen sink, and one near to the water heater. Nothing happened in the first two years, and then one day, I heard some noise coming from the other side of the house. I searched around and suddenly realized that it was the leak alarm! I run to the water heater and saw the utility room (connected to the guest bedroom) was flooded with the water from my broken water heater. I dont go to the utility room ever. So it is hard to imagine if I didnt have this alert, how my guest bedroom will look like by the time I discover this leak. The second time was a few months after that incidence, the alarm went off in the kitchen area. My kitchen sink was leaking... The product itself is not high-tech. There is a medal wire sticking out from the bottom of the box, and it will set off the alarm when in touch with even a little amount of water. When you wipe the wire dry, the alarm will stop. So you can easily test the product when receiving them (I did). I think this is a must-have for any house hold. You spend small, but can potentially save big.