> you may have to think both about protecting your data by technical means, and about not angering the agents more than you plan to

That's the same problem with technical solutions to crime.

I come from a very dangerous city and I used to have a car that needed a PIN to work. You could turn then engine on and drive but after a minute if you didn't input the PIN it would turn off without warning and start blasting the alarm. The idea being that if the car was stolen the thief would be stranded not far from home unsure about what's happening. Great technical solution but it ignores that a lot of the time the car is stolen with you in it (in a kidnapping, for example). Having the car shutoff in the middle of a highway next to a panicking guy with a gun and trying to remember a PIN is not a situation you want to be in, so I just had the PIN number written down on the dashboard, which worked very well when I was eventually kidnapped and just pointed at the piece of paper with the number.

In phone terms, that's the $5 wrench problem. The elaborate tech is not relevant if you can be simply coerced somehow to bypass it.

Again in phone terms, maybe bring a blank phone through that border.

And there's the problem that if the PIN or worse a biometric version of this becomes remotely well known you've now created an incentive for a car thief to kidnap people even if they only want the car.

As one does. Why, six of the eleven times I've had my car stolen, it was a carjacking with myself or my family member in it.

What city was this, if you don't mind me asking?

Why are you staying in this place?

(Is this in South Africa?)