display this by means of a flashing red light which will operate as long as the electrical power source functions and this light will be easily seen by the staff upon ordinary walking in the corridor the signal may of course be supervised from a central in another way e g by means of cabling video or similar when authorized use of the alarm system occurs the alarm system can be stopped by e g a special reset card i e an off position card which is available only for authorized staff this reset card must of course be kept in a secure place and in another place than the emergency keys in this way the authorized staff will be able to use the emergency key without triggering a permanent alarm this is an alarm which although it is recorded will be terminated at once unauthorized persons which use the emergency key or make attempts to pick the lock or emergency opening mechanism will trip the alarm the system demands secure storage of the reset card an example of an embodiment of the system described is shown in the fig1 and 2 fig1 shows the outside of the door lock faced against the corridor with a sign 1 a card reader gap 2 and a light emitting diode 3 an emergency opening mechanism 4 is here shown as a standard lock cylinder but it could be formed in another way e g as a window which must be smashed or similar fig2 shows a sectional view vertically through lock case and sign where an indicator 5 may be a magnetic sensor micro switch optical eye or something else the indicator 5 is connected with control electronics 6 which further is connected with a.