Switching device for checking the closed position of a folding door

A switching device for checking the closed position of a swinging door mounted in a frame, the device being of the type in which a signal is produced by the closing movement of the door relative to the frame comprising

• an infrared transmitting device in one of the door and frame;
• an infrared receiving device in the other of the door and frame for producing a distinguishable signal when infrared energy is received;
• circuit means including a switching transistor coupled to said transmitting device for selectively activating said receiving device to produce an alarm-activating signal in the presence of infrared energy;
• means defining a plurality of ports in each of said door and frame to permit passage to infrared energy therethrough, said ports being aligned in pairs when the door is closed,
• said transmitting device being arranged to project energy and said receiving device being arranged to receive energy through at least one but less than all of said pairs of ports;
• a pane of bullet proof glass transparent to infrared energy covering each of said ports, each said pane being undetachably fastened to its associated port;
• conductor means for interconnecting said transmitting and receiving devices;
• and
• means undetachably fastened to said door for providing a conduit for said conductor means when said door is closed and open and to inhibit tampering with said conductor means.