According to Google employees on the Soli team, the chip will know when it enters an unsupported region. This is so it can disable the Motion Sense feature that comes with the phone.
While it will be approved in many regions, there are some countries where Google was not able to secure the support. This was due to the potential of the radar chip interfering with the navigation systems in those regions.
When the Pixel 4 enters a different country, the Soli chip checks for approval
Google wasn't able to secure the approval for Motion Sense in every country. Because of this, some countries won't get the Pixel 4.
That won't stop people from traveling, though. So Google had to figure out a way to disable the Motion Sense feature in this situation. What it came up with was essentially having the Soli chip check for approval.
This happens when users who purchased the Pixel 4 in a region where Motion Sense is supported enters a different region. If Motion Sense is supported in the new country as well, nothing changes.
If it's not, the Soli chip disables Motion Sense. Meaning there's no real way around keeping it active if you travel somewhere that approval wasn't granted.
Soli uses cellular triangulation to check for unsupported regions
Motion Sense turning itself off might seem like magic, but it's not. Google says that Soli uses cellular triangulation to determine if you're in a country where Motion Sense wasn't approved.
This actually seems like a rather elegant solution to what could have been a big issue. Google obviously thought about this enough though to prevent it from becoming a problem.
And, just as Soli disables Motion Sense, it should enable it again once you're back in a supported country. Giving you full access to its benefits once more.
While this does render the feature useless, you can still use the phone and everything else that it offers. All that means is that you will need to interact with certain functions without the slick hand waves, and only for as long as you're in that region.
There's no telling if Google will ever get approval for the feature in the currently unsupported regions, but it's likely safe to assume that won't be happening. Not unless those countries overhaul the systems that Motion Sense would interfere with, or Google figures out a way to make it so interference wouldn't happen.