This circuit uses invisible infrared light to detect the movement of people through the door. A short beep will be generated when the infrared beam breaks. So it is ideal to monitor the passages in ...

This circuit can be built from readily available low-cost components, some of which may even be hiding in your junkbox! The indicated value of 22 Ω for resistor R1 causes an average current of about ...

[Sylvio] decided to buy one of the cheap alarm systems you can find on the internet to have a look at its insides. The kit he bought was composed of one main motion sensor and two remote controls to ...