Boardburner2:
Further to that , my gadget uses an rfid tag reader, any problems using these in the states ?
Im pretty sure they are not tested.
An RFID reader is an intentional emitter and so must have FCC testing. There are two stages to this. First you need it testing in an FCC approved test house, that will cost about £1000, then there is the FCC filing, you need an FCC approval number that is about another £1000 and then that reader again at about the same price.
Last times did this was 2009.