Luggage Security Alarm

While travelling in public transport such as buses or trains, people usually carry expensive belongings and are quite insecure about their safety. Even though after locking the luggage thoroughly, there is always a worry about it.

To solve this problem here is a simple luggage security alarm circuit based on NAND gate. When somebody tries to steal the luggage, the circuit will give a warning alarm. An audio visual indication can also be provided by connecting it to the relay.

This project circuit can also be used in home to prevent the attempt of burglary as when somebody tries to open the door, the loop breaks and the alarm starts sounding.

The project is built around CD4011 with components like LDR, variable resistor, capacitor, transistor and relay.. It generates a warning beep when somebody attempts to open the locker. To understand the working you should know about the truth table of NAND gate which is as follows-

INPUT	INPUT	OUTPUT
A	B	Y
0	0	1
0	1	1
1	0	1
1	1	0

The truth table of NAND gate shows that the output will remain HIGH until any of the signals is LOW. If both the signals go HIGH then in that case the output will be LOW.

The output of circuit depends on Pin 5. When power supply is connected to the circuit the voltage at pin 5 is zero as loop is intact. Therefore voltage at pin 4 becomes high which is connected to pin 1 and 2 which are also high. As the truth table of NAND gate says that if both the inputs are high then the output is low , so we will receive LOW at pin 3 of gate 1 which is connected to pin 12 and 13 making them also LOW. Hence, pin 11 goes HIGH making pin 8 and 9 also HIGH and voltage at pin 10 as LOW. As a result transistor connected to it through resistor will not be energized and we will not receive the alarm.

Now imagine somebody tries to take the luggage therefore the loop connected to it breaks. When loop breaks pin 5 and 6 goes high and reverse action take place. As a result pin 10 will become high and the transistor will start conducting and we will an alarm will sound. This alarm will not go off until the loop is intact again.

In this circuit we can use battery of 6-15V depending on the rating of the relay. The buzzer can also be connected directly without using Relay. The relay is used in the circuit because if the alarm to be connected works on AC an extra isolation would be needed from sudden current spikes. A diode is used with the relay because any reverse-voltage spike can short-circuit at source and they can do any damage to the circuit.