There’s nothing more welcoming than a door opening for you.【C1】_____the need to be touched to open or close, automatic doors are essential in【C2】__disabled access to buildings and helping provide general【C3】_____to commercial buildings.

Self-sliding doors began to emerge as a commercial product in 1960 after being invented six years【C4】_____by Americans Dee Horton and Lew Hewitt. They【C5】__as a novelty feature, but as their use has grown, their【C6】__have extended within our technologically advanced world. Particularly【C7】__in busy locations or during times of emergency, the doors【C8】_____crowd management by reducing the obstacles put in people’s way.

【C9】_____making access both in and out of buildings easier for people, the difference in the way many of these doors open helps reduce the total area【C10】__by them. Automatic doors often open to the side, with the panels sliding across one another. Replacing swing doors, these【C11】__smaller buildings to maximise the usable space inside without having to【C12】__the way for a large, sticking-out door. There are many different types of automatic door, with each【C13】__specific signals to tell them when to open. 【C14】__these methods differ, the main【C15】_____ remain the same.

Each automatic door system【C16】_____the light, sound, weight or movement in their vicinity as a signal to open. Sensor types are chosen to 【C17】_____ the different environments they are needed in. 【C18】_____, a busy street might not【C19】__a motion-sensored door, as it would constantly be opening for passers-by. A pressure-sensitive mat would be more 【C20】_____ to limit the surveyed area.

【C5】