If I undestand correctly, being selective would be identifying whether a radar signal is a cop or not based on its actual frequency. Saying, for example, athat 10.400-10.425 GHz is reserved for company A making doors, and 10.450-10.475 GHz is reserved for company B making police radar
But, there is no reliable way to say "this part of K band is for doors, and this part is used by cops" etc. While the FCC must liscense each device that sends out a RF signal, it would be nearly impossible to create a detector that has a catalog of known frequencies that cops use vs alarm systems or doors, let alone keep that catalog updated.
