Reply to DIY laser controller

I want to make a controller, that sends a note when a laser beam is interupted.
I tought i saw these lasers on sparkfun but i can't find them anymore.

Basicly i want i to act like a sort of button.
When the beam is interupted it should be "pressed" and when it's not interupted, not pressed.

If something like that doesn't exist, i've got another idea, Just a regular laser and a photocell with a comparator atatched to it, wich is followed by an invertor (NOT-Gate).

If you guys would give me a link, or a opinion on my backup plan it would be great.

ps. Sorry for my grammar mistakes and words that i may have translated wrong