You should never voluntarily hand your phone to a police officer.

It’s going to become increasingly tempting for the cops to ask and for you to comply, especially as more and more states adopt digital ID systems that allow driver’s licenses and state IDs to be added to Apple Wallet on iOS and Google Wallet on Android. Californians can now add their driver’s licenses and state IDs to their iPhones and Apple Watches in addition to Android devices, making the state one of seven — alongside Arizona, Colorado, Georgia, Maryland, Hawaii, and Ohio — to allow storing digital IDs through Apple’s system.

These particular digital IDs are so far pretty limited. California’s are for use at “select TSA checkpoints” and participating businesses, for instance — they aren’t meant to be used as identification in traffic stops or other police interactions, which means users are supposed to continue carrying their physical IDs. But other states — including Louisiana and Colorado — have rolled out their own digital IDs that can be used during traffic stops and other police interactions, which may have fewer privacy protections. And Apple’s vision for Apple Pay has long been explicitly to replace your entire wallet, which means that eventually, these IDs will be meant for use during police stops.

No matter what, teaching people they can add their IDs to their phones means some people will inevitably leave the house without physical ID, and that means creating the opportunity for cops to demand phones — which you should never, ever do. Technical details of your digital ID aside, handing your phone to a police officer grants law enforcement a lot of power over some of your most intimate personal data.

In Riley v. California, the Supreme Court unanimously held that police need a warrant to search through cell phones, even during otherwise lawful arrests. But if you hand over your unlocked phone to a police officer and offer to show them something, “it becomes this complicated factual question about what consent you’ve granted for a search and what the limits of that are,” Brett Max Kaufman, a senior staff attorney in the ACLU’s Center for Democracy, told The Verge. “There have been cases where people give consent to do one thing, the cops then take the whole phone, copy the whole phone, find other evidence on the phone, and the legal question that comes up in court is: did that violate the scope of consent?”

If police do have a warrant to search your phone, numerous courts have said they can require you to provide biometric login access via your face or finger. (It’s still an unsettled legal question since other courts have ruled they can’t.) The Fifth Amendment typically protects giving up passcodes as a form of self-incrimination, but logging in with biometrics often isn’t considered protected “testimonial” evidence. In the words of one federal appeals court decision, it requires “no cognitive exertion, placing it firmly in the same category as a blood draw or fingerprint taken at booking.”

The court said its ruling shouldn’t necessarily extend to “all instances where a biometric is used to unlock an electronic device” because Fifth Amendment questions “are highly fact dependent and the line between what is testimonial and what is not is particularly fine.” And as Recode pointed out in 2020, a defense attorney could argue that any evidence found this way is illegal and should be suppressed — but that’s a risky bet. “It’s fair to say that invoking one’s rights not to turn over evidence is stronger than trying to have the evidence suppressed after the fact,” Andrew Crocker, a senior staff attorney for the Electronic Frontier Foundation, told Recode for that piece.

You might be thinking at this point: you’ve got nothing incriminating on your phone! And an officer may well come to that conclusion. But they could also find something you didn’t even realize was there. “There are a lot of laws on the books, and if a prosecutor or police officer decides to go after you, are you sure you didn’t do anything?” Jay Stanley, a senior policy analyst with the ACLU’s Speech, Privacy, and Technology Project, told The Verge. “You’re only opening yourself to abuse, to errors, to mistakes. There could be a coincidence that placed you at the scene of a crime that you weren’t even aware of.” Even if you assume most officers are acting in good faith, there are plenty of documented instances of officers abusing their power and facing no legal repercussions. There’s no reason to preemptively hand over something that could be used against you.

There are some minor protections built into Apple and Google’s current systems — you can display an encrypted ID without fully unlocking your phone, and various authorities can scan your ID wireless if they have special readers. But you don’t want to be in a situation where you’re searching the web for the technical and policy details of your digital ID system when a cop demands your phone — you’re much better off handing over your license.