Water Alarm is a battery powered alarm similar to a smoke detector but this one detects water. It sounds an 110db alarm for up to 72 hours once water is detected. The unit is small and discrete and is pet and child safe. You can put it anywhere, especially where you've had water issues before. If you have a downstairs bath that you hardly ever use, put one of these water alarms in the shower and it will sound if the main sewer starts to back up. These alarms can be placed practically anywhere.