I remember reading about the vietcong using very elaborate underground chimneys to eliminate smoke - but it wasn't so much 'undetectable' as undetecable from a helicopter gunship doing 200mph'
On the ground the idea was to confuse the location of the actual fire and release the smoke and cooking smells away from the tunnels they were using. It wasn't undetecable, just less obvious.
I think the ideas only really worked if you were permanently dug in.
"Donít take life so serious, son, it ainít nohow permanent." Walt Kelly