We have those. But compelling a finger print is much easier than a password.

Exactly. Biometrics are awful because

1. they can be compelled by force,

2. they can be physically collected, unbeknownst to the owner,

3. they share all the risks of digital passwords, including being leaked,

4. they can't ever be changed, even when known to be compromised by 1, 2, or 3.

Much better to have 2+ passwords for deniable secrets.

    A unlocks the device. Most people only have this one "normal" password.
    B unlocks the device plus secret b, maybe some extra kinky porn so people feel they've found your real secret.
    C unlocks the device plus secret c, your real secret, maybe Bitcoin wallets or that novel you've been working on forever.

If there's software on the device that does this, it's only evidence that 1+ secret dirs might exist. It should be impossible to tell that c exists, let alone compel its disclosure via C. But if b is quite stale, that's at least a hint that c might exist.

or even better ... a kernel backdoor to expose hidden encrypted filesystems and false physical disk size reporting, with a specific userspace trigger (eg: open the password manager, when this password is selected destroy the hidden filesystem(s); when this other app is opened and the phrase "X y Z" is typed, expose the hidden filesystem as a disk to userspace).

You can go on forever with this stuff, especially if you have root on the device. Which gives you some clues about the true purpose of laws like this and who thinks they are useful.

Nobody really does that in practice although. Something that catches %99.9 is pretty good!

Have it as a second factor. Just make it harder for police to confiscate devices. U2F keys are great but they can be confiscated too along with your password. Fingerprint or face is possible to copy but much harder. Most police don't walk around with 3D face scanners.

Also make software self-destructing with a warning, i.e. if the user chooses it at installation time, all data will be destroyed automatically by the OS if they move the device off-premises. Make the setting unchangeable after installation time.

Police won't want to destroy evidence, so they'll have no choice but to leave it on premises.

I'm not trying to enable criminals, but rather enable whistleblowers and to not succumb to unreasonable new laws, and keep unethical searches for bad reasons in check.

> Also make software self-destructing with a warning

This is not how forensic analysis works. Data is copied to read-only supports before any attempt of access is made.

no, what you do is make a second password for the same account that opens a secret profile with different access.

A biometric is a username, not a password.

It's an authentication factor. It's not a username because you can change those.

(For twins they're more likely to have different usernames than different biometrics.)

No, it's an identification factor.

Tomato tomato. It’s all vectors and Boolean logic at the end of the day. Or if you want to get fancy, then add weights and step ups.