For use with fresh or saltwater aquariums or terrariums containing reptiles & amphibians. To install, simply separate the two halves. Place the digital thermometer on the outside and the other half inside the tank. No wires or probes extend from the unit. Approximately 2" x 2" x 1-1/4" thick. Extends 5/8" out of the tank. Large 3/4" tall numbers. Reads 0º to 99º Fahrenheit. Operates on (1) standard LR44 1.5 Volt Alkaline watch battery (included). For use on tanks with glass 1/4" thick or less.