Silicon Valley's smartphone snitching has come to an end. Apple and Google have promised that the latest versions of their mobile operating systems make it impossible for them to unlock encrypted phones, even when compelled to do so by the government. But if the Department of Justice can't demand that its corporate friends unlock your phone, it may have another option: Politely asking that you unlock it yourself, and letting you rot in a cell until you do.

In many cases, the American judicial system doesn't view an encrypted phone as an insurmountable privacy protection for those accused of a crime. Instead, it's seen as an obstruction of the evidence-gathering process, and a stubborn defendant or witness can be held in contempt of court and jailed for failing to unlock a phone to provide that evidence. With Apple and Google no longer giving law enforcement access to customers' devices, those standoffs may now become far more common. "You can expect to see more cases where authorities are thwarted by encryption, and the result is you’ll see more requests that suspects decrypt phones themselves," says Hanni Fakhoury, an attorney with the Electronic Frontier Foundation. "And by requests, I mean demands. As in, you do it or you’ll be held in contempt of court."

In some cases, the Fifth Amendment's protection against self-incrimination may block such demands, under the argument that forcing defendants to unlock their phone would compel them to testify to their own guilt. But the few cases where suspects have pleaded the Fifth to avoid decrypting a PC—the legal equivalent of a smartphone—have had messy, sometimes contradictory outcomes. "This is not a settled question," says James Grimmelmann, a professor at the University of Maryland Law School. And it likely won't be, he says, until more appeals courts or the Supreme Court consider the issue.

Grimmelmann does, however, offer one general guideline for whether a Fifth Amendment argument will keep the cops out of your locked phone and you out of jail: "If the police don’t know what they’re going to find inside," he says, "they can’t make you unlock it."

In 2011, for instance, a Florida man identified only as John Doe had two computers and five external hard drives seized in a child pornography investigation. (He was never charged with a crime, so his name was not revealed in court.) Doe had encrypted his drives with TrueCrypt, and took the Fifth to avoid having to unlock them. The court ruled that forcing him to surrender his password and decryption keys would be the same as making him provide self-incriminating testimony, and let him off the hook.

In a Vermont case in 2009, by contrast, a child pornography defendant named Sebastien Boucher made the mistake of allowing police access to his computer following his arrest at the Canadian border. They found child pornography, but after seizing his computer realized the portion of the hard drive containing the incriminating files was encrypted. They demanded Boucher cough up the password. He refused, pleading the Fifth. A judge ruled against him, calling the contents of the computer a "foregone conclusion." The police didn't need Boucher's "testimony" to get the files, in other words—they only needed him to stop obstructing access to them.

Not every case is so clear-cut. In 2012, a Colorado district court ruled that Ramona Fricosu, a defendant in a mortgage fraud case, had to surrender the password to her locked laptop after she was heard on a recorded phone call telling her co-defendant husband that the incriminating evidence was encrypted. That call was enough to nullify her Fifth amendment argument. As with Boucher, the judge ruled that she give police access to the files or be held in contempt.

"Even if you have a Fifth Amendment right to avoid compelled decryption, you have to be very circumspect in how you behave," warns Grimmelmann. "The court may only find in favor of defendants who have been very careful about not talking to law enforcement and who have been very well advised in keeping in their head down."

Depending on where the law settles, it could leave few cases where the Fifth Amendment protects locked phones at all. Former prosecutor and George Washington University Law Professor Orin Kerr argued in a piece for The Washington Post on Friday that merely confirming that a phone belongs to you and admitting you know the passcode circumvents the Fifth Amendment. "If the phone’s in the suspect’s hand or in his pocket when the government finds it, that’s not going to be hard to show," he wrote. He pointed to the Boucher case. "Under the relevant case law, that makes all the difference: Entering in the password no longer raises a Fifth Amendment problem."

Using Apple's TouchID to unlock a phone represents another way to compel suspects to open their phone. As defense attorney Marcia Hofmann wrote for WIRED last year, a fingerprint isn't "testimony." So demanding a suspect extend their hand allows for no Fifth Amendment defense. Other biometric unlocking mechanisms would be equally vulnerable. "We can’t invoke the privilege against self-incrimination to prevent the government from collecting biometrics like fingerprints, DNA samples, or voice exemplars." Hofmann wrote. "The courts have decided that this evidence doesn’t reveal anything you know."

Despite all of this, Apple and Google's pledge to stop unlocking devices on behalf of police still represents a victory for privacy, argues Chris Soghoian, technologist at the ACLU. Now users may at least have the choice to deny the government access to their phones, even if it means jail time, rather than leave that decision to Apple or Google. Journalists protecting their sources, for example, sometimes spend months or even years in jail rather than provide their private data to investigators. That self-sacrifice is an option only if Google or Apple doesn't rat them out first.

"Maybe this is still a positive step," Soghoian says. "Instead of leaving it to a company that doesn’t have your best interests at heart, you can make the choice: You can turn over the keys, or you can face the consequent of not doing so."