Why not build something quiet simple.
Build a small wood box around one of those cheap small CO2 bottles that has a pin that when the top is depressed it punctures the top of the bottle venting the gas. Similar to the CO2 ones that you can buy. You can get 25 packs of those bottles for like $10 at a ANY crappy tire too.
Personally if you yourself are not willing to set the mouse trap off IN your own hand before setting this out in the feild I really wouldn't recommend the mouse traps. Specially when there are so many other ways out there. Like fire alarms for example. Stick a batter in one, wire it so that when the top is pressed it goes off! Only need to modify the test button really. Unless you're smoking out in the feild real close to the ground. Yeah I'm looking at you Stalker! :P just kidding. That way its easily reuseable. Not to mention that there are ways to rewire them up to have trip lins and all sorts of different applications to them.
Anything that can hurt someone is probably not the best way to go. And yes I know LUTNIT we are shooting at each other here. But you wanna go crawling along and roll to cover to take this thing on your ear; nose, neck, face, etc etc.?
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"The hydrogen economy car from the people who brought you the '
Hindenburg'" - Glen Foster
Condoms do not guarantee safe sex any more. A friend of mine wore one and was shot by the woman's husband!