As far as I am aware the snooper S3 which is what I think you mean is a GPS type and no false alarms will be received. I have a snooper s4 and get no false alarms, all the GPS ones are very similar, the main factor is the manufacturers data base and how up to date it is. I have had no problems with snooper, it has warned me of every site I have come across.
As for hard wiring it in, I wouldnt do this myself, I have mine mounted on the windscreen and plugged into the cigarette lighter, it is not a problem and I can remove it from view when parked up and also use it in any vehicle I like.