Laptop alarm circuit diagram

This is a laptop protection circuit that protects your laptop or netbook from being stolen. Fixed inside the laptop case, it will sound a loud alarm when someone tries to take the laptop. This highly sensitive circuit uses a homemade tilt switch to activate the alarm by tilting the laptop case. The circuit uses readily available electronic components and can be built on a small PCB.

This laptop/notebook protector is powered by a 12V micro battery for remote control devices. The ICTLO71 (IC1) is used as a voltage comparator with a voltage divider consisting of R2 and R3 providing half the supply voltage at the non-inverting input (pin 3) of IC1. Only when the probe in the tilt switch comes in contact with water does the inverting input receive a higher voltage through the water activated tilt switch.

When someone tries to take the laptop case, the unit is in vertical position and the tilt switch breaks the electrical contact between the probes. The output of IC1 immediately goes high and triggers the monostable IC2. The low output of IC2 triggers the pnp transistor (T1) and the buzzer starts beeping. Build the circuit as compactly as possible to make the unit matchbox size.

Make a tilt switch using a small (2.5 cm long and 1 cm wide) plastic bottle with two stainless steel pins as contacts. Fill the bottle two-thirds full with water so that the contacts do not form an electrical pathway when the tilt switch is in a vertical position. Make the bottle leak-proof with adhesive or wax. Secure the tilt switch in a horizontal position inside the circuit enclosure.

Mount the device inside the laptop case in a horizontal position using adhesive. Use one micro buzzer and one micro switch (S1) to make a compact gadget of this circuit. Keep the laptop case in a horizontal position and turn on the device. Your laptop/notebook is now protected from theft.