This Fluval digital thermometer is a 2in1 gadget! It will measure your aquarium water temperature and room temperatues using wireless technology…. so no probes or messy wires are needed! Measures accurately to within 1 degree and allows you to select celcuis or farenheit. The big display makes reading very easy. How it works…. just remove the adhesive backing and press the thermometer firmly against the outside of your aquarium. All you need to do is just make sure that the sensor on the back of the unit is below the water line and touching the glass.