Abstract: An electronic door unlocking system comprising an electromagnet within a door adjacent to a deadbolt to retract the deadbolt upon energization of the electromagnet and an associated spring to advance the deadbolt into locking orientation with the recess upon a deactivation of the electromagnet. Also provided is a key with a long part formed with a first computer chip at its free end and a short part spaced from the long part. A sensor assembly is provided in the door knob with an interior component with a second computer chip contactable with the first computer chip of the long part of the key. The sensor assembly has an exterior component with a plurality of apertures adapted to allow the passage of the long part therethrough. The interior and exterior components are spaced at a distance essentially equal to the difference of length between the long and short parts of the key.