Color Tracking a Red Laser Height I'm making a Laser Harp.
The application needs the position of the hand along each of the laser beams to modulate a sound synthesis or modify the properties of a sampled instrument.
I'm wondering if doing a Color Tracking with OpenCV will do.

Make the beam visible with fog machine.
Segmenting the image for each beam.
Measure the height of the beam.
PROFIT.

Other way can be using an infra-red light sensor like Infusion Systems - ReachClose v3.1
What method is more accurate and fail-proof?
Any other ideas?
Diagram3
I can only say something about the computer vision part.

If your doing color tracking you have to take different lighting conditions into consideration, although it will be easier with a laser (compared to other things) since it at least have the same color.

If you are to use this device professionally you should have a delay about 20ms else it will be noticeable. This forces you to use a high speed camera of at least 100fps (10ms per frame) to have time for processing and sending the sound through the amplifiers.

Since you are only tracking straight lines I would recommend to first filter out everything but the laser-color and then hough transform it to find all straight laser lines. And as a final step implement an ad-hoc method to find where the laser ends shouldn't be that hard.