Pennsy,

You asked a good question and I think you are getting bad answers. What
your friend wants to do is get proof that smoke in the apartment comes from
tobacco as opposed to other sources of smoke which can also stain walls.
Here's some info on a story from several years ago
http://www.electricnews.net/news.html?code=9362073 It seems such devices are
possible, the question is whether anyone makes or sells them. Your friend
should poke around on Google or write the folks in Dublin.

Dave M.