Circuit stuff

[cholin]

I want to make some laser motion sensors, and most of it seems pretty simple, EXCEPT:

1)  Photoresistor, Photodiode, Phototransitor (which one and what ratings?!)

2)  If I wanted to have like 8 of these connect to a master board type thing (like in those movies where an LED on a map lights up) where would I put the diodes in the circuits?  I want the lasers all getting power from the central box, which is easy, but if a circuit is broken, voltage is lost, inverted into a positive signal, and then back off ot the main box to power an LED...

If ya need a picture let me know, its really a simple thing Im just not good at diode-placement I guess.