Per a FB post in the past month, my former PD's dog just finished training to detect guns and gunpowder. I'm friends with his handler and if we ever connect again I'll see if the dog detects it on me or not. Since I hate going into MA except for hit-and-run doctor appointments, it's really unlikely that I'll make that connection however.
These are known as Probable Cause Terriers. As long as they indicate on a car in any way, they pass the course.