
What do you mean by "police band" - there is no such thing.

Anyway, radar detectors work in shared bands.
If you applied your test, all of those radar operated door
openers in malls would be illegal.

One of the great problems here is that there are too many
ill-educated (read illiterate) people making too many laws
about subjects on which they are incompetent - there may well
be laws refereing to "police bands", they are almost certainly
local in scope (state or county) - created by well-meaning,
but incompetent idiots.

Unfortunaltely, laws do not have to be sensible (or even enforceable).
Lawmakers exist to pass laws - and will continue to do so, until
the day where you are faced with death for not doing X, and
amputation of all your limbs for doing X ... the choice will be yours.

Note: no smiley.