to move upwardly this applies tension in the linkage spring 39 and quickly rotates the disc 35 to its position as shown in fig2 that is to say the retroreflector snaps into its reflective position accordingly infrared rays entering the tube through the aperture 33 and aligned on the mirror will be reflected back at the associated scanner 26 39 which detects the reflected rays indicating that the contact blade 16 has entered the jaw of the stationary contact 18 and has opened the jaws to assume a proper operation of the hv switch in the specific application the infrared signals generated by the scanner were pulsated infrared signals and they provide the advantage of preventing the scanner to be affected by ambient infrared rays that may come from the sun indirectly or from any other light source such as electric arcs referring now to fig4 there is shown another application of the semaphore of the present invention and in this particular instance for detection of the pressure level of a gas in a high voltage circuit breaker or a level of insulating oil in a transformer or bushing or any other variable that may be interesting to be monitored as herein shown the linkage would include a pressure gauge type device 50 having a connection 51 which disengages with a connection 52 associated with the retroreflector 53 if the pressure in the guage 50 falls or increases above predetermined limits the connections 51 and 52 would disengage and cause the retroreflector 53 to assume a horizontal position by suitable spring biasing means not shown to prevent reflecting the infrared rays 54 directed in the aperture 55 of the housing 56 many other applications of the detecting device of the present invention.