Have had fruit flies in the lab and they tend to travel home (what a pain). The best trap I have used so far is to set out a short glass with apple cider vinegar and place either a small spouted funnel on top (spout downward but not actually touching the vinegar) or you can make a paper cone with a small opening at the tip. The little flies are lured inside with the vinegar (apple cider does work best at least for me) and get inside but have a hard time getting out. Eventually they drown.