This is not all true. It is the opposite of what you are saying. Have to let the local office where register at know 21 days before you go (which I would not do, but I would if on probation ). Nobody in the United States would even know you are in out of the country until you get back. I have gone on 2 trips since they started the 21 day requirement and both time they never said a single word about if I informed the local law enforcement or not, and this was at San Francisco airport. The thing about informing the any agency in the country you are visiting. That is the stupidest thing I have ever hear. Why tell anybody anything when there is no way for them to know about it before you told them. If you get through immigration and you are allowed to enter then you are clear for that visit.