i'd say it happens it may not be ethical but why not?
especially if there have been complaints about you or you have a criminal record, or someone at the DWP or job centre is looking for promotion, so many things.
in the UK we know people who are fraudulent are put under surveillance so how many people have the spied on that were innocent but thought to be not innocent at some point? it must happen, they have to record, spy etc to prove there fraudulent so what about the ones who were just investigated but no evidence found?
things like mind control beams and watching through TV are science fiction.