Laser alarm for game/road rally

I am currently designing a road rally that has a spy theme. I am using my sister's garage as a "high tech fortress" that must be "broken into" by each of the teams. The plan is to use a DIY laser beam alarm system (similar to what Kipkay demonstrates in this video:

I will use mirrors and a photo sensor to bounce the mirror all over the garage. Then my thought is to use a smoke machine to get it slightly smokey inside so the laser beams will be easily visible. The team will have to navigate through the laser maze without triggering the alarm. Once they reach the end of the maze, they will be able to get the next clue.

But the idea is to somehow penalize a team that triggers the alarm.

The difficulty lies in the fact that this has to be a system that runs on its own for the evening of the game, resets itself if the alarm gets triggered, and somehow indicates to a scorekeeper that the team triggered an alarm.

One thought that I had was to use a sonic alarm that automatically gets triggered if the laser is blocked, but immediately shuts off once the laser re-establishes. This should be pretty easy. The second component would somehow "record" or trigger a recording of some sort showing that the alarm went off.

And, of course, it can't be too overly complicated. Tall order, huh?

My wife thought to just make it a novelty, and not penalize anyone for going through it. But this is a race, and I would rather have people try to see if they could do it, as opposed to just walking through and getting the clue because there is no recourse in order to save time.

Anyway, if anyone has any thoughts to do this, I would appreciate it.

Etienne 72772, welcome to the forum Wowwwwwwww that sure IS a tall order. What is the build-up? Do you mean after each and every stage of the maze the system has to trigger the alarm and reset itself or at the end of the maze only?

I have been pondering it a little bit. The laser system should be pretty easy, I could probably knock out a few like the one Kipkay instructs here: http://www.metacafe.com/watch/1133002/ protect_your_home_with_laserbeams/

Here is my thought: I will set up one or up to three separate laser beams that reflect a number of times off mirrors on the sidewalls from the front of the garage to the back. This will give a number of beams across the garage to have to avoid.

My thinking is to have it to use a simple photocell switch - when the laser hits the photocell, the alarm is silent. If it is interrupted, the alarm sounds.

Then use a rudimentary computer program that changes the screen color (but can't be seen until you travel all the way through the garage). The computer has a microphone. When the alarm goes off, the computer screen color changes from one color to another. If the alarm sounds off again, it switches to the next color. Finally, if they hit the alarm let's say, 5 times, the screen goes black. When they are done getting the clue (or whatever they are supposed to get from the screen, they have to hit a "reset" button, which gives then 20 seconds or so to get out of the garage, and will not record the alarms until the time is up.

They still get the clue on the computer screen, but they also have to report what color the computer screen is. This will tell me how they fared through the maze, and how to dock points.

can you see the red laser use in this system with a black light