Shower Mate - 100 % waterproof with an oversize suction cup back and a hanger so it can be used in a shower or placed on a Mirror or standard wall. These clocks are designed to ensure that when washing your hands, it is done for a full 20 seconds as recommended by the CDC for good health. Great on a Boat or any high splash area or high humidity location. The dial is designed to help young people or anyone to continue to wash their hands for the recommended time. Uses 1 AA battery (not included) Dimensions 4" Diameter x 1.8" D