There is a very nice video of the in-line system linked to this page:

http://blog.tsa.gov/2008/03/how-we-d...screening.html

In DEN, if you bag doesn't go to the room on the east side of Level 6 (behind the Frontier ticket counters) it is assumed that passengers have not declared a weapon. If they find it and it wasn't declared, you may lose the weapon to the Denver Police Department and be fined by the federal government.