This compact alarm system alerts you with an audible warning if someone approaches your briefcase with the intention of taking your valuables out of it. It is a battery- operated device that may be tucked away discretely in a nook or cranny inside the briefcase. The circuit has a low number of components and is straightforward to put together. A piezo-element that is typically found in buzzers is the primary component of the circuit. In reaction to either pressure or vibration, the piezo-element can be used to generate electric signals. A couple of tens of nanofarads constitute its capacitance (nF). When a voltage is supplied, the piezo-element rapidly charges and stores the charge until it is mechanically disturbed. This behavior is analogous to that of a capacitor. Any kind of mechanical vibration will cause the charge on the piezoelectric material to reorganize and, as a result, energy will be released. The voltage that is generated across the piezo-sensor is what causes the IC LM358 to be triggered. This component is a low-power transducer amplifier. The integrated circuit LM358 requires 9 volts to function and features two independent high-gain op- amps that together have a massive DC gain of 100 dB. In this case, the integrated circuit is set up to function as an inverted Schmitt trigger so that it can transform incoming signals into a shaped output waveform. A threshold voltage is established by presetting VR1, which occurs at the non-inverting input

threshold of IC1. While the piezo-sensor is linked between the inverting and non- inverting pins, one end of feedback resistor R1 is connected to the output of the IC and the other end is attached to the non-inverting input (pin 3). The output of IC1 is low when it is in the standby mode, which occurs when the signal from the piezo-sensor is low. The feedback resistor R1 raises the non-inverting input voltage to a level higher than the upper threshold voltage (UTV), which is around 1.8 volts. The charge that is stored in the piezo-sensor is released when it is briefly tapped, causing the inverting input voltage to rise to a level that is higher than the positive input and causing the output to drop. When anything like this takes place, the voltage at the positive input drops through VR1 and reaches the lower threshold voltage (LTV). Due to the absence of the input signal, the voltage that is present at the inverting input at this same instant is quite low. This results in a rise in the output, as well as a beep from the buzzer. The output of the IC will decrease whenever the input value is greater than the UTV, but it will increase whenever the input value falls below the LTV. The hysteresis of the Schimdt trigger is what differentiates the LTV and the UTV in terms of their functionality. The buzzer will continue to sound for a few seconds after being touched by the piezo- sensor, even if the hand is removed from the sensor. This is due to the fact that once the output swings high, even a little reduction in voltage at the negative input has no influence on the circuit. When it has been started, the change in status cannot be easily undone. Construct the circuit on a general-use printed circuit board that is as little as feasible, and then house it in a compact housing. The diameter of the piezo-sensor need to be between 10 and 15 millimeters at most. You can attach it to the main unit by sticking a tiny wire that is insulated and some glue to the underside of the handle of the briefcase. A battery with 3 V is all that is needed to power the circuit.