DIY Laser Alarm

Open the door that you will be protecting with your laser beam alarm --- for example, the front door or a door leading to an attached garage. Place the red laser pointer against the bottom edge of the door with the reflector facing toward the door frame. Tape the red laser pointer to the door with strips of duct tape.

Place a motion detector alarm on the floor next to the door frame. Plug the motion detector alarm's power cord into a wall outlet for power. You can use an extension cord to extend the reach of the power cord if a wall outlet is not close enough.

Rotate the motion detector alarm so the sensor on the front is lined up with the reflector of the red laser pointer. The distance between the two does not need to be taken into consideration, since a laser beam is being used.

Set the "Sensitivity" or "Gain" knob or sliding switch (depending on the make) to its highest setting. Set the "Volume" knob or sliding volume switch (depending on the make) to its highest setting.

Press the "On" button on the red laser pointer to activate the laser beam. Realign the sensor on the motion detector alarm if the laser beam is not hitting the sensor.

Press the power button or slide the "On" selector switch (depending on the make) to activate the motion detector alarm. Leave the area. If the door is opened, the sensor on the motion detector alarm will detect the movement of the laser beam and sound its alarm.