Do not hand your phone to a cop. Ever.
This is old tech. I had a boss in the 90's who had an ignition interlock thing on his car and it wouldn't start unless he blew clean.
I found out about it when he was trying to find someone at work to blow into it so he could go home.
It wasn't until a couple of days later that I put it together that he managed to get so drunk during working hours that he couldn't drive himself home.
Hand sanitizer, fragrances trip interlock breathalyzers all the time, I wonder what could possibly go wrong?
Also who’s gonna pay for the towing and the reset/ recalibration after a false positive and why?
You could imagine a scenario where putting a phone into driver's license mode disables Face Unlock, and maybe even pauses all push notifications like text messages, and therefore is more secure because it forces people to put their phone into a password mode. So it'd actually encourage people, when talking to law enforcement, to increase their security settings.
I don't know if these companies currently do it like this, but they should.