Have you seen the "Follow Me Thomas" toy?
Now I have, thanks
My niece got one of these, and it's the reason I wanted to try to get my bot to follow a laser. Instead of a laser(can't give those to 3 year olds) this toy comes with a red flashlight, and the train follows the circle where the beam is shone. I believe there is a sensor behind each bumper. I figured it used photo-resistors specific to red light. Do you think it just uses regular photo-resistors and covers them with transparent red plastic? The toy works very well, even following the light on red carpet or wooden floors and in brightly lit rooms.
Either color filters or they just use them plain. If there's a much larger amount of light where it shines, it doesn't need to be color sensitive. You could try with a bright white flashlight (it should work anyway, as there's red in the white) and with a green filter in front of the white flashlight - if green light doesn't work, it indicates red color filters. For testing, any piece of (resonably green) clear plastic should do.
Perhaps you can see it with your naked eye, as red filters would cover the distinct pattern of the CdS resistor.
To follow a LASER dot, you might wanna decollimate the LASER to a wider spot, to make it easier to follow.
Most pointers have a notch in the LASER head where a small coin or similar fits. If it's not sealed with glue or thread lock, it can be twisted/turned to collimate (parallelize the beam). When I use a pointer for such stuff, I usually make the spot as wide as around 5..10cm in diameter at a ~1m distance from the head.
Modulating the LASER beam and making the sensors ignore light from unmodulate sources will make it far better behaven.
To modulate it and keeping the switching speed resonably, set the low part to a point where it is just "lasing" (beyond that current, the light will just be like a weak red LED) and set the high part to te max. current it uses, with the voltage and internal resistance of the button cells it normally uses.