Radar detectors usually do emit some radio as a byproduct of how the receiver works. Plus it lets the radar detector companies sell radar detector dectors to the cops. And upgraded radar detectors to the chronic speeders that can detect the dectector detectors. Etc.

AFAIK, it’s not about emissions or reception, it’s about increasing the LEO coffers via traffic fines.

It may be described as a signals concern but that’s simply window dressing.