Of course, why would the police be testing your doorknob, out of the hundreds of millions of doorknobs? They would have to have some reason to think that testing your doorknob would reveal something interesting.The informant who just touched the door perhaps. This standard makes it way too easy to set someone up for a search.
-Eric
Suppose some doped-up burglar tries your door, finds it locked, and leaves behind traces of drugs on the knob? You report an attempted burglary, the cops test the knob, and you get arrested? This lowers my respect for the cops a little more, and it was pretty low to start with.