Can they make me unlock my phone with my face or fingerprint?

The distinction courts have drawn is between something you know and something you are. A passcode is arguably testimonial because it discloses the contents of your mind. A fingerprint or a face has often been analogized to physical evidence — like a handwriting sample or a blood draw — which generally isn't protected the same way.

The practical consequence is counterintuitive and worth stating plainly: the more convenient unlock method may be the less protected one.

Not every court has drawn the line the same way, and the reasoning has been criticized on the ground that the outcome — access to the same contents — is identical either way. The area is genuinely unsettled.

There's a straightforward point underneath the legal uncertainty. Most phones allow biometric unlock to be disabled quickly, and most allow a passcode-only mode. Knowing how to do that on your own device before you need to is worth two minutes.