My latest project has been transmitting audio/sound over a cheap laser pointer. I found the original plans for this here.

The parts I used are:
1. Laser pointer level from Target
2. Cadmium-Sulfide Photocells (Radio Shack part 276-1657)
3. Audio output transformer (Radio Shack part 273-1380)
4. battery holder for 1 AA battery
5. battery holder for 3 AA batteries
6. Audio source ( I used the line out of my laptop)
7. Headphones
8. small piece of a dowel rod.

I picked the Target laser pointer level because it was the easiest to hack. First take the dowel rod and put a small nail in one end. Attach a wire to the nail. Put the dowel rod into the tube that holds the battery, then use a rubber band to hold it in place. Second attach a wire to the base of the laser pointer.

Take one wire from the laser pointer and attach it to one of the 1k leads of the transformer (blue wire). Take the second wire and attach it to the positive lead of the 3AA battery pack. The laser pointer usually runs on 2 AA batteries. With the transformer, the laser pointer would barely light up so I used 3 AA batteries instead.

The audio source needs to be attached to the 8ohm side of the audio transformer. Attach one line to the red wire and one to the white wire.

We now have a laser transmitter.

For the reciever take the 1 AA battery holder. Connect the positive lead to one end of the photocell. Take the negative lead and connect it to your headphone. Connect the other lead of the headphone to the other end of the photocell. We now have a reciever.

The sound goes into the transformer. The transformer then causes the laser to modulate. When the laser light hits the photocell, the photocell changes the amount of electricity going to the headphones. This causes the sound.

have fun.