The invention relates to a locking cylinder with a longitudinal housing, said housing containing a control sensor for triggering an electrical switch for detection of introduction of a key into the cylinder, said sensor being slideably mounted parallel to the axis (A) of introduction of the key, the front end section of the sensor, which may be pushed by the key, cooperates with the housing means to form a ramp to cause a displacement of said front end section in a direction inclined with relation to the axis (A) between a lower idle position and an upper trigger position in which the housing (2) further contains a switch trigger means, in contact with the rear end of the sensor, said trigger means being only able to move parallel to the axis (A).