If you're arrested then the cops can tie you, grab the keys and unlock your door "and there's literally nothing you can do to prevent it.".
Also some guy can just make a copy your key (pretty trivial) -- heck people can even break your door bypassing the key altogether.
In the phone case, they don't need a warrant if your authentication method is literally your face.
Depends on the country. Not everywhere, including western Europe, is this true.
For one, there are tons of loopholes, from border searches to "evidence of criminal activity" (dead easy to "prove" for a black/latino/poor person and have the court agree), and unless you can afford a good lawyer, good luck trying to prove your rights were violated:
https://en.wikipedia.org/wiki/Warrantless_searches_in_the_Un...
http://www.npr.org/2011/05/16/136368744/in-warrantless-searc...
Not to mention that warrants are not that difficult to obtain either -- except in the movies.
If all 3 of these are true, you need a warrant (at least in the US). Doesn't matter if the keys, or in this case your face, are right there. The fact that you locked your phone with something the cop doesn't normally have is enough to require a warrant.
Detective: "Is this yours?"
_Suspect glances in the direction indicated, phone unlocks._
Detective: "Nevermind, I got it from here."
-----
At least TouchID required physical assault to get you to unlock the phone. FaceID on the other hand can be defeated with perfectly legal attention grabbing techniques.
Without a warrant: No information taken from your phone by the police is admissible.
With a warrant: A judge can compel you to unlock any device with a biometric lock, regardless of what sort of biometric lock we are discussing. Fingerprint, iris scan, or face, it simply does not matter.
Fruit of the poisonous tree is a legal metaphor in the United States used to describe evidence that is obtained illegally.
For example, if a police officer conducted an unconstitutional search of a home and obtained a key to a train station locker, and evidence of a crime came from the locker, that evidence would most likely be excluded under the fruit of the poisonous tree legal doctrine.
https://en.wikipedia.org/wiki/Fruit_of_the_poisonous_tree
Border agents operate under a different set of rules and have been searching mobile devices without a warrant or even probable cause.
However the ACLU and EFF have filed a new lawsuit challenging this behavior, now that the Supreme Court has ruled that the police cannot conduct warrantless searches of cell phones inside the US.
Doesn't (or can't) law enforcement also use parallel construction (based on information obtained without a warrant)? I believe the point about what's admissible is not as clear cut as you state in a single sentence.
And even there, would this stop a police force who routinely abuses, beats up, or even kills innocent people on the street for no or imagined provocation?
Nobody's saying that home security is good. The point the parent was making is that, even with a "liveness test", compared to other biometric identification, this is a regression from fingerprint-based authentication for the iPhone.
You think they can force you to look at it ("engage" with it) but not touch the phone?
Honestly, the easiest attack would just be to ask me about my dogs. 99.99% chance I'll unlock my phone, pull up pictures and show them to you (easy grab) or just hand you the phone and let you browse through them.