Absorb humidity and prevent rust or mildew in gun safes or other enclosed areas. Moisture-control crystals change color when unit needs recharging. Recharge by plugging into 110V electrical outlet. Safeguards firearms and other valuables from mold and mildew. Eliminates humidity in enclosed spaces up to 333 cubic feet. Quick-connect bracket makes mounting unit easy in gun safes, closets or pantries. Removes humidity without electricity or batteries. Color-shifting moisture-control crystals signal when recharging is necessary. Simply plug in to dry out crystals and recharge unit for renewed effectiveness. Contains no harmful chemicals – child, pet and home safe.