I tried the moon conspiracy theory and was mauled to within an inch of my life!
Yes, yes, I read the whole thread, but I still believe they didn't. We will see.
Those bar code scanners has a laser emitting diode, a mirror (sometimes a real mirror, I mean glass with metallic coating, other times a polished metal plate.
The beam is reflected in the mirror and thus projected to the scan area. The mirror moves in a between certain angle to project the beam over a surface. Old models (10 yrs or so) used motors to move the mirror. Newer models, otoh, use an electromagnet to force magnetic attraction-repulsion over the metal plate, and so move it, and (they) can do it faster.
The bar-code to scan reflects the light over a linear ccd, where as you know, you get back where the light was reflected and where not.
(Most Symbol models work like that).
There are some other without laser, just with a row of leds and a linear CCD. Those are far cheaper, but also have a fixed read length.
The ones that have just one led and one photo-transistor are the optical pens.
If you modulate the laser beam you can recover your information after some hops (reflections), that is not a problem !