No, the NES Zapper does both. It detects light level changes frame-to-frame as you describe, but it also uses the CRT beam timing to determine _where_ on the s

No, the NES Zapper does both. It detects light level changes frame-to-frame as you describe, but it also uses the CRT beam timing to determine _where_ on the screen a target was hit. http://en.wikipedia.org/wiki/NES_Zapper http://en.wikipedia.org/wiki/NES_Zapper Also, even if the NES Zapper worked only on luminosity deltas, it could work on other types of displays -- but the response time (lag) of the display would have to be frame-accurate in order to detect the hit in time before the software moves on. (Software could compensate for lag, of course, but actual NES games don't.)