SmartPool Pool Eye Universal Swimming Pool Alarm With Remote Receiver - PE23 For use on above ground or in ground pools up to 20 X 40 feet Advanced immersion technology allows it to read surface waves and sub-surface waves for objects 15+ pounds Features battery powered poolside base unit and in-home receiver that works up to 100 feet away Sounds 85+ dB at poolside and also features a magnetic key for activating and resetting Automatically resets after 3 minutes, and has a low battery indicator