It’s a rite of passage to techies the world over: unlocking, or “jailbreaking,” a cell phone to make it usable on networks other than the one to which it was initially attached. But after Saturday, such an act—which can, for instance, make a Verizon iPhone compatible with the T-Mobile network—may be illegal. In October, the Library of Congress invalidated a copyright exemption for unlocking cell phones, but that exemption expires Saturday, leaving the door open to repercussions for such actions. Beginning today, consumers may receive warnings from carriers if they are found unlocking their device. For tech geeks, the word “jailbreak” just got a little more sinister.