I've been doing the occasional search on this, ever since reading a while back about passwords, security, biometrics and such after reading an article about how law enforcement can simply unlock your phone using your own biometrics. Forced entry into digital devices by using a person's biometrics to unlock the content without their consent (and at times without a search warrant) may or may not be legal. Why? Because unlocking a smartphone can constitute testimonial evidence.
Turns out that under current laws you have far more protection of your digital information under the laws if you use passwords. Passwords in conjunction with PKI would be even more secure, but most people don't use, or have the capability to use, PKI with things like cell phones or tablets.
Biometrics, however, do not carry the same levels of protection under the law when it comes to accessing your digital information.
Let's say you are arrested and law enforcement wants to search your phone. (Let's not consider a search warrant here, but just the physical accessibility of this.) If you have the phone password protected, they cannot access it (easily, anyway) unless they have the password. They cannot force you to give up the password. And if the only person who has that password is you, then it's pretty safe against a search. Safe enough, hopefully, to at least get you to the point of an attorney working for you who understands the applicable laws and will be able to fight for you accordingly.
However, if your phone is protected by biometrics (fingerprint or facial recognition, for example), then you have no protection against law enforcement involuntarily using your biometrics to access your locked phone. Biometrics are not (as yet, anyway) afforded the same protections as something you would have to actually tell someone else would be. They can physically apply your finger to the phone or present your face to your phone's camera to unlock it.
It's a fascinating legal issue (well...at least as fascinating as a non-attorney can find it).
But fingerprints as ID for the scope of this thread? That's not a legally protected issue, being that it's for identification purposes.