Thank you for the information gentlemen. I couldn't find anything online other than CO's used commercially. I'm well aware of it's dangers. As far as dead mice in the walls, I don't know how to avoid that with any kind of fumigation. My wife's shop is where she does art glass work. Most kinds of fumigation will leave a film on the glass which will screw it up when fired in a kiln. I got curious about CO from something I read.
It looks like we'll have to keep trapping.
Get a flip n slide bucket trap or make something similar. I used to make bucket traps out of a piece of tig rod and a beer can. I'd put a ring of peanut butter around the middle of the beer can, which was suspended on a tig rod axle across the bucket. You've got to drill a couple holes in the ends of the can and the top rim of the bucket.
Use a scrap of wood to make a ramp up to the top of the bucket. The mice would jump to the can, which spun on the tig rod and fall into the bucket and drown.
I now just buy these.
Flip N Slide Mouse Trap - Made in USA
