Are there any electronic device which can buzzer when third person enters?

Thread Starter


Joined Oct 24, 2023
Medical Shop has authorised entries and trying to add additional security measures like if some third person enters in the designated area, then the buzzer should alert. Is there already some electronic device using which we can achieve this?


Joined Jan 23, 2018
The effective method would use a TV camera to monitor the area and a computer to monitor the number of human forms moving around. If entry were possible through only one path, then a camera could watch that and detect those entering without a specific badge. Rather doable but not really cheap. For cheap, an array of PIR motion sensors and when there is motion in more than two locations send an alarm.
The unknowns are the dimensions of the area and how much the people move in normal operation.


Joined Aug 21, 2017
1.possibility - cheap camera sends the live video to PC with LabView runtime. LabView is capable to make the face recognition. As soon the wrong face - means alarm.
2.possibility - take the RF tag or card. Tag may be read to 30-80 cm distance (however altering RF field over the health limited value may be read over 2 meter distance). Card may be read in close proximity to reader. And counter on door counts how many people are in the room. If card count not pass to room count = alarm.
3.possibility - each authorized person keeps in the pocket IR diode with 555 generator on certain frequency. Frequency list is created by means of LM567 tablets. As soon the people count in room not pass the activated 567 detector channel count = alarm
4.possibility - the same with ultrasound frequencies and the same LM567 based detector.
5.possibility - granted the access persons carry the lip on the shirt front pocket. On the lip is glued passive catafoting element for IR range. In the walls sit the weak infrared heaters and room is covered with infrared camera. As soon the picture contains less the "light brights" as the person count in the room = alarm. Sorry, but IR camera here is rather expensive thingy.