This feature, along with the fact that the diskette is not square, prohibit incorrect orientation. File cabinets can fall over if too many drawers are pulled out. For some file cabinets, opening one drawer locks all the rest, reducing the chance of the file cabinet tipping. Automobile controls have a mistake-proofing device to insure that the key is in the on position before allowing the driver to shift out of park. The keys cannot be removed until the car is in park.
Warning lights alert the driver of potential problems.
These devices employ a warning method instead of a control method. What used to be a driving error is now the proper braking procedure. New lawn mowers are required to have a safety bar on the handle that must be pulled back in order to start the engine. If you let go of the safety bar, the mower blade stops in 3 seconds or less. Cicuit breakers prevent electrical overloads and the fires that result.