How to Make a Laser Burglar Alarm

Though it has more high-tech components than a traditional burglar alarm, a laser burglar alarm still uses the same three basic elements: a siren, a trigger and a power source. In the case of a laser alarm, the trigger is a beam of light, which activates when something crosses it and sets off the siren. You can make a laser burglar alarm of your own using a few simple components found at your local Radio Shack.

5-megawatt 12-by-30mm laser 3.2v AC adapter Battery-powered 12v siren or buzzer 9v battery Black plastic tube Photocell Tape, adhesive, or Velcro strips Mirrors

Instructions

- 1
  Attach a 5-megawatt laser to a 3.2v AC adapter. This will allow you to power the laser through an outlet in your home.
- 2
  Slide a photocell into a short length of black tubing. This keeps ambient light away from it and increases the effectiveness of the laser.
- 3
  Connect the photocell to a battery-operated siren or buzzer. Do not insert the battery itself yet. Otherwise, the siren will go off while you are still working. You also may need to glue the tube onto the siren housing to keep it steady.
- 4
  Mount the laser to one side of the entryway you wish to protect, using Velcro or similar adhesive to hold it in place. Mount the photocell/alarm array to the other side, making sure that the laser light shines directly into the photocell.
- 5
  Connect the battery to the siren or buzzer. It should now go off whenever the laser light is broken.
- 6
  Add mirrors to deflect the laser light and create more security beams. By placing the mirrors in the path of the beam and angling them in precise directions, you can cover more entryways just as effectively. Just make sure that the beam terminates at the eye of the photocell, so the alarm will still go off.

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