This is a misunderstanding. That's the area in which the border patrol has jurisdiction to can conduct very limited searches of vehicles and operate checkpoints without individualized suspicion in order to enforce immigration law. It does not allow searches of electronic devices.

There is a separate border search exception at the point a person actually enters the country which does allow searches of electronic devices. US citizens entering the country may refuse to provide access without consequences beyond seizure of the device; non-citizens could face adverse immigration actions.

To be clear, I do think all detentions and searches without individualized suspicion should be considered violations of the 4th amendment, but the phrase "constitution-free zone" is so broad as to be misleading.

With ICE on the prowl, I’d have thought ‘Constitution Free Zone’ a fitting description of how they operate.