Pro Tip: if you insist on enabling thumbprint identification for convenience’s sake, and are ever arrested, immediately power off your phone. When the authorities turn your phone back on, they won’t be able to unlock it without your password.
In the case of an iPhone, no, that’s not the thing to do. It takes too long. (Hold down power button, swipe). What you want to do is reboot your phone, which is a much simpler action. (Hold down power & home buttons for 2+ seconds and release.) It’s less obvious.
However, if you’re arrested, the chance of you being able to retain control of your phone are very close to zero. So you’re going to want to not wait until after you’re arrested to do this. But if you are before you can do this, and you can’t reboot the phone, there’s another solution: flub the fingerprint check. Flub it three times (use the “wrong” finger or don’t line it up right) and bang, you have to use a password.
Also, while password managers are a decent compromise, ultimately, they’re just as vulnerable as not using one. that master password has to be human memorable after all and if the authorities that arrest you aren’t particularly ethical, “rubber hose decryption” is still the fastest method.