Laptop anti-theft protector circuit diagram

The laptop anti-theft protection circuit here can protect your important netbook/laptop from being stolen. Basically, this is a mini security alarm generator. Secured inside the laptop case, it is sure to sound a noisy alarm when someone tries to grab the laptop. This very sensitive circuit utilizes a homemade tilt switch to turn on the alarm system by tilting the laptop case.

The circuit utilizes off-the-shelf parts and can also be easily built on a small piece of general purpose PCB or Vero board. This circuit is powered by a 12V micro battery used in remote control devices.

IC TLO71 (IC1) is used as a voltage comparator with a voltage divider consisting of R2 and R3 providing 50% of the supply voltage at the non-inverting input of IC1 (pin 3). Only when the probe in the tilt switch is in contact with water does the inverting input get a higher voltage through the water activating the tilt switch. When the tilt switch remains in the horizontal position, the inverting input of IC1 receives a higher voltage than its noninverting input, and the output continues to be low.

CD4538 (IC2) acts as a monostable multivibrator with timing factors R5 and C1. Considering the displayed value, the output of IC2 remains low for three minutes. The CD4538 is a monostable multivibrator that fires accurately and is more reliable than the famous timer IC 555. Its output goes high on power-up and low when the trigger input (pin 5) receives a low-to-high transition pulse.

The circuit device is horizontally fixed in the notebook chassis. In this position, the water within the tilt switch properly shorts the contacts, so the output of IC1 continues to be low. Since trigger pin 5 of IC2 is low, the alarm system generator remains silent in standby mode. When someone attempts to grab the laptop case, the device is in a vertical position and the tilt switch breaks electrical contact between the probes. Instantly the output of IC1 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 so that the unit is matchbox size. Use a small plastic bottle (2.5 cm long, 1 cm wide) with two stainless steel pins as contacts to make the tilt switch work. Fill the bottle two-thirds full with water so that the contacts do not create an electrical path when the tilt switch is in the vertical position. Make sure the bottle is leak-proof with adhesive or wax.

Hold the tilt switch in a horizontal position inside the circuit housing. Use adhesive to mount the device in a horizontal position inside the laptop case. Used in conjunction with a micro buzzer and micro switch (S1), the device is small in size and light in weight. Hold the laptop case in a horizontal position and turn on the circuit. Your laptop is now safe.