This timer is an "old school" mechanical timer. Ideal for simple 24 hour control of electrical items such as lights, pumps etc. I have 3 units controlling such items to operate at night and to take advantage of lower off peak electrical rates. They have proved to be extremely reliable, operating for many years with no issues. The unit has a single NO contact. It also has a small rechargeable backup battery that maintains the timer in the event of power loss.