The police will ask you if the PIN unlocks the phone before using it.

Refusing to answer questions IS one of the rights that the US government mostly honors.

Well, these days especially at border police don't care about "rights"

That's missing in this entire conversation. This all sounds like it's 2016 or something

This is not a "these days" thing. Most rights essentially being abrogated at the border is a thing we've had for many decades now. In particular, no non-citizen has the absolute right of entry, and border agents have discretion bordering on insane when it comes to not admitting people or temporarily detaining them. Worse yet, this being the case, the job attracts the kind of people who relish the petty power trip. I've seen this many times back in 2010-2011 when I was traveling regularly as a non-citizen between US and Canada.

I don't think denying entry to non-citizens abrogates anyone's rights.

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Under US law, you have a nearly absolute right to not answer police questions.

Yes of course. But their use of the PIN will likely only occur if you answer, which many people will. This is a common setup in interrogations.

the utah cops definitely would, based on whats been released from the rwckless ben bodycam footage

I belive this only applies if you are a US citizen and not a visitor.

Up in the air. SCOTUS didn't decide on this specific right. They did rule on other constitutional protections though, sometimes granting, sometimes denying them to non-citizens. It also depends if you're just arriving or already are in the US. For example, illegal immigrants who jumped the border fence have more rights than legal immigrants who didn't leave the airport yet.

It unlocks the phone.