I am going to show how to make your own theft alarm.
This laser-triggered theft alarm is useful for many purposes. This theft alarm also includes a 555 timer IC monostable circuit for persistence of the trigger.
This alarm costs only 2$ for all the stuff. Because of this reason, it is considered one of the cheapest alarms in the world.
You can use some mirrors to make the laser reflect and increase its protection.
You will need:
5mW laser pointer
I have also included the schematic for easy understanding.
Note: the parts may vary according to the newer version and all the unnamed resistors are of value 1 kΩ