If you call the bomb squad to report a bomb under your car but as a technology-inclined person/geek know full well it's a GPS receiver then you're committing all sorts of illegality there.
If you think that it's FBI/DHS device (ie if your skin color is between latte and espresso, or your name as an 'Al' at the front) then call local law.
Back when I worked for a defense company our cars were checked with mirrors on sticks everytime we went to work, we had special police numbers to call if we ever saw any suspicious activity around our cars or received a suspicious package at home.
Although they weren't very understanding when I was away on a trip and my wife opened a package containing a microcontroller I ordered - and started an alert!