Casotec 7 Oz Automatic Light When Pour Water LED Light Up Drinkware Plastic Tumbler Cups This cup is environmental protection transparent shine cup when pour into liquid (water, beverage, beer, etc) , it will light up and flash immediately, very magical, suitable for celebrate, party, bars, gifts and so on. Water induction cup, if no water in the cup, it will not light up. Suitable for: bar, discos, restaurants, leisure, party, friends gifts, etc. Power: button cell X 2 (included). To Replace Batteries: Unscrew the battery compartment door located on the bottom of the base, place new batteries in the battery compartment and screw on the battery door.