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The electric overhead garage door opener was invented by C.G. Johnson in 1926 in Hartford City, Indiana. [1] Electric Garage Door openers did not become popular until Era Meter Company of Chicago offered one after World War II where the overhead garage door could be opened via a key pad located on a post at the end of the driveway or a switch inside the garage.
An attacker may be able to learn the code word that opened the door just now, but the receiver will not accept that code word for the foreseeable future. A rolling code system uses cryptographic methods that allow the remote control and the receiver to share codewords but make it difficult for an attacker to break the cryptography.
In the early 1980s–1990s, overhead projectors were used as part of a classroom computer display/projection system. A liquid-crystal panel mounted in a plastic frame was placed on top of the overhead projector and connected to the video output of the computer, often splitting off the normal monitor output.