How to make a laser listening device

Written by marshal m. rosenthal
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How to make a laser listening device
(Hemera Technologies/ Images)

Laser pointers are commonly used for projecting a beam of light to call attention to text or pictures as a speech or lecture is being made. You can also use a laser pointer to fashion a laser listening device because laser light can be changed by the audio waves it encounters. The procedure does not require any great skill with electronics, although you will need to use a soldering iron. Making a laser listening device demonstrates just one of the many things the coherent beam of light that a laser is made of can do.

Skill level:
Moderately Easy

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Things you need

  • Newspaper
  • Scissors
  • Ear buds
  • Wire stripper
  • Soldering iron
  • Solder
  • Cadmium sulphide photocell
  • Two tripods
  • Laser pointer
  • Duct tape
  • Laptop
  • Audio recording program

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  1. 1

    Put down some newspaper on a table. Cut off the ear bud end from a pair of ear buds using a scissors. Strip the wires at the end with the wire strippers.

  2. 2

    Heat up a soldering iron. Solder the red and white wires from the ear bud to one of the contact pins on the cadmium sulphide photocell. Solder the black wire from the end of the ear buds to the other contact pin on the cadmium sulphide photocell.

  3. 3

    Duct tape the cadmium sulphide photocell to the top of the tripod.

  4. 4

    Go into your backyard. Duct tape the laser pointer to the top of the other tripod. Adjust the tripod so the laser pointer is aimed at one of the windows on the back of your house.

  5. 5

    Place the other tripod at a 45-degree angle from the window at the back of the house. Adjust the tripod so the cadmium sulphide photocell is aimed at the window.

  6. 6

    Turn on the laser pointer. Adjust the tripod that is holding the cadmium sulphide photocell so the reflected beam of the laser coming from the window strikes the cadmium sulphide photocell. Plug the ear bud jack into the headphone plug of the laptop. Run an audio recording program on the laptop.

  7. 7

    Walk back into the house and talk to yourself next to the window that the laser pointer is aimed at. Stop talking after a few minutes have gone by.

  8. 8

    Go back into the backyard and turn off the laser pointer. Turn off the audio recording program on the laptop. Play back the audio recording program and listen to your voice that has been recorded by the laser listening device you have made.

Tips and warnings

  • Wear protective goggles to protect your eyes when adjusting the laser from the laser pointer.
  • Don't aim the laser pen at a person's face because the beam can cause damage to the eye.

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