You do not have to activate a signal booster in order to use it. The FCC does require you to register it for their records.
All of the signal boosters that we sell do not require any sort of activation to begin boosting signal.
While you do not need to activate your signal booster to use it, if you're operating a signal booster in the United States, you are required to register it with your cell carrier. This registration does not impact how the signal booster functions, rather it tells the carrier that a booster is operating at your location, in the event that they see any interference on their network and need to track down whether it was caused by a signal booster.
Rest assured, of the millions of consumer-level signal booster systems that have been sold in the United States since 2014, there have been no recorded issues of a signal booster causing interference with a carrier's network. That said, you should still register your signal booster to comply with FCC regulations.