I took apart an HF laser level, item # 54050, on sale now for $7.99. Turns out the laser (and associated drive elex) is just a little brass cylinder about .375" dia x .570" long with two wires coming out of it. Connect wires to 3 volts (a couple of AAA batteries), and ya got a laser beam.
I haven't played with laser pointers much, but this little pill seems pretty bright and agreeably small. The spot was easily visible on a tree trunk (not birch!) at range of 50 feet in overcast daylight today. Seems like this would be very easy to use in a variety of gadgets with various housings and power sources.
It lights at about 2.4 volts, reaches 29 mA at about 2.5 volts, current (and brighness) is constant from there to 3 volts. With that draw, a single 2L76 lithium cell .457" dia x .425" h (max dimensions) would run it for 3 or 4 hours. The slightly larger 1CR2 lithium (.614 dia x 1.013 h) would run it for many hours, maybe 20. And, of course, it can run it off a couple of AAA's if space isn't an issue. I know some pointers use the little LR44 "watch" batteries, but I don't think it'd run very long with those. 29 mA is a heavy draw for them. Using the 2L76, the whole package might be about 1/2" dia x 1-1/8" long.
The bareass laser seems to emit two beams and produce two spots close together on the wall. I expect a little field stop could take care of that if it were an issue. I didn't go out to the tree to measure the spot diameter, but I'm sure it's considerably smaller than a CO2 pistol can group at that range. Well, let's see.....at 10 feet it looks like it's about .050 or .060 dia, hard to tell because it's so bright on the scale.
I'm thinking about making something to stick on daughter-in-law's CO2 squirrel-zapping pistol. She can shoot just fine but marking the little bastards with the "red spot of doom" might be fun.