You know those scenes where the leatherclad catburglar sprays something to make the burglar alarm lasers visible?
I need that. For just about the same reasons.
I’m doing a Cub Scout presentation on lasers, and while I have several fog machines to choose from, there’s a concern the fog will set off the fire alarm…not a good thing when borrowing a school cafeteria for the evening.
A spray bottle to make a mist of water? The hard part would be finding one that makes a very fine spray. Can you test this ahead of time?
ETA: Or better, one spray bottle per Cub Scout. And some paper towels to clean up the water.
Small blackboard, chalk and erasers.
Remember eye protection for the Cubs! Another trick to make the laser beam visible is to hold an index card in the beam.
Burning some incense could work without disrupting the alarms, or pick up a small smoke pen to direct smoke locally to show up the laser.
I’m keeping the event strictly sub 5 mw for eye protection. I’ll have a projector set up to show them what more powerful lasers can do. There are 3 or 4 red lasers, a blue one, and a green one that, honestly seems like it’s pushing the envelope from a power standpoint…that one won’t be used on the hands on demonstrations, and there will be a parent at each station while the kids are getting some hands on time. Believe me, the safety issue is a big one, and kind of a bummer as I originally wanted the ‘popping a black balloon in a clear one’ to be one of the high points…but that’s just to much power in a room with 15 kids and another 10 adults.
I like the blackboard and erasers idea…unfortunately, they’ve been replaced with dry-erase boards and projectors. 
Water mist isn’t fine enough, I tried, which resulted in this thread. 
I watched a commercial kitchen hood being installed (while I drank beer at the bar). The crew used a hand-held smoke generating device to show the hood in action.
Ultrasonic humidifier. For the fog to last any time/distance from the machine, you’d need high ambient humidity - so this would work very well in Key West, not so well in southern Utah. At the very least, you could still shine the laser through the outlet stream close to the humidifer.
Alternative: a large fish aquarium in which you have only a bowl of water with a chunk of dry ice in it. The aquarium will retain the fog-laden air, allowing it to grow nice and dense.
Maybe the humidifier would work inside the aquarium? Heavy/cool air would stay in the aquarium, where the humidity would increase to the point that new droplets from the humidifier would persist for longer periods of time. If you happen to have an ultrasonic humidifier, you can do a quick test in a five-gallon bucket. Set the humidifier in there, turn it on, and come back in 20 minutes; if the bucket is full of fog, then this will work, and now you just need to find an empty aquarium you can use.
Not a bad idea, I think we may have one in the basement somewhere.
If they’re anything like the Cub Scouts I remember, they’ll be able to come up with a half-dozen ways of making smoke on their own.
Not without setting off the fire alarm!
How about dry ice dropped in warm water?
A twenty pound sack of flour and a cherry bomb.
You’ll give the presentation they’ll be talking about the next day.
I’ve used “Cloud in a Can” for this effect.
I purchased it here:
http://setshop.com/light-control/gelsdiffusion/set-shop-diffusion/12329-diffusion-in-a-can.html
Five or Six years ago Mythbusters tested this and decided something like to see the beam you had to have so much powder or mist in the air that it stopped the beam. The effect you see in the movies doesn’t happen in reality.
Now, they may have just been using ultra violet lasers used in alarm systems and a visible light laser would work fine. I’m not sure.
Silly string.
No, wait, that’s tripwires.
How about some fine powder, like talc or graphite? Just do it over a plastic sheet or some newspaper to make it easy to pick up, otherwise someone will slip and give the scouts an opportunity to practice their first aid skills 
Cigarette smoke?
Are you sure a fog machine would even set off the alarm? I’ve seen them used indoors all the time in haunted houses and stage productions.
Does the green laser have an actual higher output or is it just seeming too bright to you?