This is laptop / notebook protector circuit to protect your laptop or notebook or netbook from being stolen. Fixed in-side 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 through tilting of the laptop case. This circuit uses readily available electronic components and can be built on a small PCB.
This laptop / notebook protector is powered by a 12V miniature battery used in remote control devices. IC TLO71 (IC1) is used as a voltage comparator with a potential divider comprising R2 and R3 providing half supply voltage at the non-inverting input (pin 3) of IC1. The inverting input receives a higher voltage through a water-activated tilt switch only when the probes in the tilt switch make contact with water.
When someone tries to take the laptop case, the unit takes the vertical position and the tilt switch breaks the electrical contact between the probes Immediately the output of IC1 becomes high and monostable IC2 is triggered. The low output from IC2 triggers the pnp transistor (T1) and the buzzer starts beeping. Construct the circuit as compactly as possible so as to make the unit matchbox size.
Make the tilt switch using a small (2.5cm long and 1cm wide) plastic bottle with two stainless pins as contacts. Fill two-third of the bottle with water such that the contacts never make electrical path when the tilt switch is in vertical position. Make the bottle leak-proof with adhesive or wax. Fix the tilt switch inside the enclosure of the circuit in horizontal position.
Fit the unit inside the laptop case in horizontal position using adhesive. Use a miniature buzzer and a micro switch (S1) to make the compact gadget with this circuit. Maintain the laptop case in horizontal position and switch on the unit. Your laptop / notebookis now protected from stealing.