We have long recommended that you should not use any biometric (fingerprint, facial recognition, etc.) method to unlock your smartphone. Use a PIN, or better yet, a password to unlock your device. Courts are all over the map as to whether you can be forced to unlock your phone with a password. Our own state of Virginia has ruled that you can be compelled to use your fingerprint (something about you) to unlock your phone but not your password (something you know). Other states have gone the other way. Don't forget that federal courts are different from state courts too. Even law enforcement knows that you can use a dead person's finger to unlock their device if they are recently deceased.
Techdirt reported on another case involving whether password production can be testimonial. The Indiana Appeals Court says forcing someone to unlock their phone violates the 5th Amendment. So add one more state to the list. Even though all courts aren't clear about being compelled to unlock your smartphone, we'll still go on recommending not using Touch ID (or something similar) to unlock your phone.
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Digital Forensics/Information Security/Information Technology