The Flood Buzz™ Pro has two metal prongs on the bottom of each unit. When water comes in contact with the metal prongs, it closes the circuit and sounds an up to 110 dB alarm. Since the Flood Buzz™ Pro comes with an integral battery that lasts for up to two years, all you have to do is place the unit next to any potential leak source. The unit is maintenance free until you replace it. For best protection, test your Flood Buzz™ Pro upon installation and replace it prior to the “Replace by” date printed on the product.