[Orin Kerr] The Fifth Amendment and Touch ID

My recent post on the legality of warrants that permit phone unlocking prompted some reader comments on how the Fifth Amendment might apply to using fingerprint readers such as Apple’s Touch ID. I think this is a hard issue, so it might be worth explaining my thinking in detail. Here are my current thoughts, with the caveat that my views aren’t completely settled and I may revisit them in the future.

Let’s start with an easy case, which I’ll label Case 1. The government orders a person to place a particular finger on a particular phone’s fingerprint reader. The Fifth Amendment is not implicated here because the person is not testifying. He is not saying anything about what is going on in his mind, so no Fifth Amendment testimony has been compelled. The police could force him to put the finger on the fingerprint reader if he were asleep or otherwise unconscious. No testimonial statement from the person is implied by the act of placing his finger on the reader.

Now consider Case 2. The police search a home with a warrant. The police find only one electronic device in the house — a single iPhone with Touch ID enabled — on the kitchen table. There are seven residents present at the house. When the police ask the seven residents who owns that phone, they all refuse to say. An officer approaches one of the residents and says: “I’m guessing that this is your phone. If you don’t go over there and unlock it with Touch ID, I’m going to arrest you for refusing my order.” It turns out the officer was right: It is that resident’s phone. The question is, does that resident have a Fifth Amendment right not to comply with the order?

Case 2 is different from Case 1, I think, because I see complying with the officer’s order as including testimony. It amounts to testimony that says, “yes, this is my phone,” or at least, “yes, this phone was set to recognize a part of my body as a means of access.” It further says: “I am familiar enough with this phone to know that the fingerprint reader was enabled and which part of me was used by me to program the fingerprint reader.”

Case 2 implies testimony because Touch ID is programmed to respond to only one body part. That choice of body part acts like a password. It’s a simple password, but it’s still a password. Most people use a finger, but they can use any of their 10 fingers. And Touch ID can be programmed to use other body parts such as the palm of a hand or even toes instead of fingers. (Very unlikely, sure — but possible.) Most people choose which body part to use based on convenience, not security. But the owner knows which body part was used and the government doesn’t, so responding to the order by unlocking the phone using the correct body part tends to show that the person is the owner.

Why might that matter? Imagine the investigation in Case 2 began when someone texted a threatening communication from a cellphone to an undercover officer. The government has reason to believe the originating phone was inside the house to be searched. The warrant authorized the government to search the house and then seize and search the phone to confirm that it was used to send the threat. In that scenario, the act of going over to the phone and unlocking it provides evidence of familiarity with and likely control of the phone. That alone isn’t enough to show that the unlocking resident sent the threat, but it’s a “link in the chain” of evidence that might support that conclusion. So I would think that unlocking the phone using Touch ID has testimonial aspects that can be incriminating and therefore trigger the Fifth Amendment.

Now consider Case 3. Imagine the police know that a particular phone belongs to a particular person. They saw the suspect use the phone to make calls and send some text messages. The suspect refers to that particular phone as “my phone,” and he gives out a number as his that rings that phone. Now imagine the police seize the phone with a warrant and want to order the suspect to use the fingerprint reader to unlock it. The officer says, “Unlock this with Touch ID, or else I’m going to arrest you for refusing my order.” Does the suspect have a Fifth Amendment right not to comply with the order?

I think the testimonial aspect of Case 3 is the same as in Case 2, but that there’s a big Fifth Amendment difference between them: Compliance would be a foregone conclusion in Case 3, while it was not in Case 2. In Case 2, the unlocking helped prove that it was the suspect’s phone. But the government already knows that in Case 3, so the foregone conclusion doctrine should apply and that should d