I'm thinking about making my own laser security system (think mission impossible). So I was thinking I'd use a laser diode to shine a beam across a doorway into a light dependent resistor that's on the high side of a voltage divider and look for that signal to go low and raise an alarm if it does.
So I've done some quick research for parts and I'm surprised at how expensive laser diodes seem to be: Do I really need to use a "laser diode" to satisfy my requirement to shine focused light across say a 3 foot gap, or is there some other component that is cheaper and gets the same effect?
Does my LDR concept on the "receiver" side of the gap make sense or is there a better way? I guess my biggest concern is that it won't respond (resistance won't rise) fast enough when the beam is broken and I'll fail to pick it up as a logic low. If that's the case I imagine what I'll want instead is something like a photo-transistor rather than an LDR.