This simple homemade circuit detects the motion of persons in the distance of 0.5 to 1m. It works on electrostatic principle. The antenna is a short piece of wire, the length is selected due to the required sensitivity. Electrostatic charge is changing as large conductive objects (including people) are moving near the antenna. The top picture shows circuit with LED, which lights up when the person or hand is getting closer to the antena and turns off when moving away. In the bottom picture is a modified circuit where the motion detection lights up the LED and the LED will remain lit until the button is pressed (left side of the image is the same as above). The sensitivity is also dependent on the C1 capacitor - lower capacity...higher sensitivity. You can also add or remove one transistor, adding one greatly increases the sensitivity, removing one significantly reduces sensitivity. When too much sensitivity, however, the LED will light permanently. Instead of LED you can connect any siren or other circuit. Supply voltage may be about 5 to 24V. Resistor R1 is for normal LED: (Vcc - 2) x 100, or supply voltage in volts minus 2, multiplied by 100 and resistance comes in ohms. Resistance is not critical. The circuit is simple, so it is suitable also for beginners. all components are the common types that are easy to find.
