Of course, the Magistrate Judge Kandis Westmore’s ruling can be overturned on appeal by a District judge in the Northern District of California in which she operates, or on appeal on the ruling’s way up the appellate chain.  Nevertheless, her ruling stands, for now.

In its essence Westmore ruled that, even with an otherwise valid search warrant, a person cannot be compelled to unlock a digital device like a cell phone with that person’s biometrics—a fingerprint, a face, or an iris, for example.

There was a technicality that itself would have invalidated the warrant: it was overbroad.  It requested authority to unlock and search any device found inside the otherwise legally searched premises, including those owned or controlled by anyone happening to be present at the time of the search, and Westmore found that request to be neither limited to a particular person nor a particular device as the 4^th Amendment requires.  That’s a 4^th Amendment failure of the warrant.

The larger principle, though, flows from a 5^th Amendment bar against forced self-incrimination violation. Westmore ruled that biometrics, when used in the context of a search—vis., to unlock a personal digital device—is no different from a personal passcode, and personal passcodes have already been ruled inaccessible to the government, even with a search warrant.  That would be forced testimony against oneself.  The owner of the device must voluntarily give up the passcode, and he cannot be “compelled” to volunteer [citations omitted].

The Court finds that utilizing a biometric feature to unlock an electronic device is not akin to submitting to fingerprinting or a DNA swab, because it differs in two fundamental ways. …the Government concedes that a finger, thumb, or other biometric feature may be used to unlock a device in lieu of a passcode. In this context, biometric features serve the same purpose of a passcode, which is to secure the owner’s content, pragmatically rendering them functionally equivalent.
…
It follows…that if a person cannot be compelled to provide a passcode because it is a testimonial communication, a person cannot be compelled to provide one’s finger, thumb, iris, face, or other biometric feature to unlock that same device.

And especially this, as I’ve argued elsewhere.

That the Government may never be able to access the complete contents of a digital device, does not affect the analysis.

Government convenience must never be allowed to override the individual liberty of an American.

In the end,

The Government may not compel or otherwise utilize fingers, thumbs, facial recognition, optical/iris, or any other biometric feature to unlock electronic devices.

It matters when, and why, biometrics are used.  The outcome here, should it survive appeal, is a stout blow in favor of individual privacy and a firm limit on Government’s authority to invade an American’s person[], houses, papers, and effects.

The magistrate judge’s ruling can be read here.