JBL DigiScan Tube is a convenient and accurate water thermometer that does not interfere with the aquarium, but is attached to a water-carrying hose. Easy to install: insert battery (included) & attach with spring clip to hose (e.g. from aquarium filter). An sensitive temperature sensor on the back of the JBL DigiScan Tube measures the temperature of the aquarium water via the hose temperature, which is identical to the water temperature. JBL DigiScan Tube fits all hoses and hose types from 12-26 mm diameter. Also suitable for silicone hoses. Preset alarm for water temperatures below 18 and above 28C.