As of Saturday, unlocking a cellphone is against US law.

The process, which allows you to use your handset with a network other than the one you bought it from, has just become illegal again as part of the Digital Millennium Copyright Act (DMCA).

Unlocking was formerly allowed under an exemption to the act, ABC News explains, but in October 2012 the the US Copyright Office and Library of Congress decided not to renew the clause and it expired on Jan. 26.

Now, you must obtain your carrier's permission to unlock your phone or face a potential fine of up to $2,500. Anyone found unlocking handsets for profit could be forced to pay up to $500,000 and may even go to jail, according to ABC.

That said, "it's not like police officers will come knocking on your door if you decide to unlock your cellphone," the New York Times assures. It's more likely suspected offenders will get warnings from phone companies.

And you can still legally purchase an unlocked phone new (though usually for a higher price), tech site All Things D points out, while some networks will agree to unlock your handset once your contract with them is up.

Networks argue that the reform is necessary to stop people selling on the phones they got free or discounted with their contract, or dealing in stolen handsets.

But consumer rights groups say phones are the user's property, and users should be able to do what they like with them.

Campaigners are petitioning the White House for unlocking to be legalized permanently, Mashable reported.

"Consumers will be forced to pay exorbitant roaming fees to make calls while traveling abroad," the online petition reads. "It reduces consumer choice, and decreases the resale value of devices that consumers have paid for in full."

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