This was at a local train show. The owner said it as a basic humidifier and water. It kind of looked more like fog than smoke, but it was a nice effect. Not sure how much the moisture would impact the layout.
Another low-tech option are either unscented incense sticks or cones. I made a couple incense burners that were designed to have the cones placed inside so it looked like smoke coming out of them. You would need to be able to collect and dispose of ash but that's it. I guess it would increase the dust in the room.
I didn't make this, but it gives you the idea.
There was quite a discussion on the Garden Railways forum about the different brands of liquid smoke that goes into one of those generators.
Some manufacturers warn people that if they don't use a particular brand of smoke fluid the generator can be damaged, but this seems to be more scare tactic than truth.
A chemist who had allegedly examined various brands of smoke fluid to see what they actually were composed of said most of them are nothing more than Mineral Oil with different scents added.
Some people have tried Tiki Lamp Oil and various other concoctions, but most of them are probably harmful to your health if you breathe too much of the vapors.
We have an IRS Building on Fire scene on our HO scale club layout with a smoke generator acquired from Micro-Mark, in which we use Mineral Oil purchased from a drug store. It makes just as much smoke as any other brand of fluid. We have a push-button on the fascia for open house visitors to push to see the smoke, so it's not on all the time.
But no matter what you use, the smoke is only going to be white and wispy, like the smoke off a cigarette.
Commercial smoke generators leave an oily residue and don't produce realistic smoke.
Using a vaporizor will give more volume - but it's water vapor. I don't know of anything that's improved by dampness.
Flashing or moving signs are good - if you can find or fabricate ones that are appropriate to your scene.
Sound can make a non-moving scene seem active. (Crew tearing up the street - recording of jackhammers and diesel compressor...) Moving machinery is even better. (Batch mix truck with rotating drum. Moving crane, even if it just swings the same box back and forth...)
Note that mechanical 'gizmos' can liven up a diorama. On a full-operating model railroad they would probably be more annoyance than asset.
Chuck (Modeling Central Japan in September, 1964)
The Wonder Bread sign would be perfect since they were a rail served customer on the Miwaukee Road C&E line that we are depicting.
Thanks Mister Beasley!
Now if the only made a Magikist Sign!
Those things smell, and they do leave an oily residue.
I would look at Miller Engineering signs instead. These provide the illusion of motion without moving parts.
http://www.microstru.com/
They have a wide variety of signs, so your son can help select them. They are flat, so they take up no space.
It takes an iron man to play with a toy iron horse.
My 9 year old son and I are building an urban ISL and have been looking to add a few bits of animation to the layout. He really likes the idea of a chimney puffing smoke. I see that we should be able to install a smoke generator into a chimney fairly easily, but I thought I read they leave an oily residue on everything. I cant seem to find the article or comment that mentioned the residue, but I would rather not ruin any of the hard work we have put into the layout for a gimmicky effect.
Thoughts?