Which laser should I get for a security system?

[mammoth_safety]

Hi everyone

I'm making a security system for fun which uses a laser to shine on an LDR (Light dependent resistor). If something passes it then an alarm goes off. I'm thinking the length of the light would be 1m. Any suggestions for lasers I should get? I was thinking the 1mw sticks from eBay but wasn't sure if it would be powerful enough.

Thanks guys.

 

[T_Warne]

So, the distance between the LDR (Light dependent resistor) and the emitter is just 1m? Why do you need to use a laser?
What wavelength is your LDR sensitive to? Why not use the corresponding LED?