Impulse relays, also known as bi-stable relays, are a form of latching relay that change the contact state with each input pulse. How do they work? Impulse relays, upon application of power, determine which position the relay is in and energizes the opposite coil. The contacts transfer and hold that position when power is removed. When re-energized, the contacts transfer to the opposite state and hold that position. Impulse relays are well suited for applications such as turning a single device on or off from one or more locations with a momentary switch or push button.