Learn in the textbookPhysical Security Measures
DefinitionAn interlock uses two doors at an entrance with a small room between them (an anteroom, 前室) so that one door cannot open until the other has closed.
ExplanationLinking the doors alone cannot stop two people from entering the anteroom together, so it is combined with designs such as a one-person anteroom or a weight sensor that counts occupants. Some setups also require a second authentication at the inner door to double-check who is entering.
AnalogyIt works like a canal lock: the near gate closes before the far gate opens, so both are never open at once.
Memory hookInter (mutual) + lock. Picture the two doors locking each other.