This dual kit comes with two electronic receiver chimes and one end-of-driveway transmitter. The driveway chime plugs into an ordinary electrical outlet. The end-of-driveway unit operates off of a 9-volt transistor battery. This chime kit includes all of the pieces necessary to set up your wireless driveway alarm system. The wireless driveway alarm includes one end-of-driveway transmitter box, one heavy-duty rubber end cap, two electronic, wireless chimes, and one Milton driveway signal hose.