Depending on the hazard being protected, a fire alarm system includes one or more of several types of alarm-initiating devices. One of these types that everyone is familiar with is the manual pull-station. These are basically electrical switches, and most can be reset after use. NFPA 72 mandates that manual fire alarm boxes be conspicuous, unobstructed, and accessible. Designers typically locate a manual pull-station, with the lever at a height of 50 inches above the floor, at each building exit. Additional pull-stations must be provided so that there is a maximum travel distance of 200 feet (61 meters) to the nearest manual fire alarm box measured horizontally on the same floor.