Abstract: An electronic key and lock system is provided which is particularly suited for use in hotels and motels to control access to the rooms of the establishment. The system includes a battery energized microcomputer controlled unit in each door which is capable of activating an electromechanical deadbolt mechanism when a magnetically encoded card bearing a selected code is inserted into a slot in that particular door, and which includes a non-contact proximity magnetic sensor for the cards. The microcomputer controlled unit has five levels of response, namely, guests, maid, master, grand master and emergency. In addition to responding to the selected code, the microcomputer is programmed also to respond to cards bearing a new code when a new guest inserts his card into the slot in the door, and of adjusting the unit to respond to the new code and not to the previous code.