GPS vehicle loggers

Are the use of GPS vehicle loggers, when the driver does not know of its presence, legal in NC? My husband is a serial cheater and I know that divorce is imminent. He has made it clear that he will emphatically deny any cheating should I try to divorce him. He has even said to me that any women with whom he cheats will also deny that they and him are anything more than friends. I do not have money to afford a PI. A friend mentioned that I should consider purchasing a GPS tracking device and place it in the vehicle that he drives. Is that legal to do? And, if so, would any information obtained from it be admissable with divorce proceedings? Thanks.

GPS tracking devices are legal in North Carolina.