Manufacturers need to pick a lane - either fully open, and then people who need it can harden their own stuff (and at least be aware of the tradeoff), or fully closed and secure.
This in-between where cars are invasive privacy nightmares that spy on you at all driving hours, and are insecure nightmares that will give up that data to anyone remotely invested, is the worst case scenario, obviously.
How could you do a clean system reset after someone had access to all installed software/data including the cryptographic keys? The information is gone, maybe the recovery partition is changed. How could you securely recover?
I'm freelancer and helped to develop some head units. I have a surprize for you: This documentation mostly doesn't exsists. Most of the time there are some chip datasheets and requirement documents, depending on the customer(car manufacturer) they are good or bad and then are some partly outdated wiki pages written down for some important special things. You learn all other stuff out of the code or from your colleagues.
Wait two years and the most knowledge is gone, except of the things that are used for the next head unit.
The biggest advantage actual developers have is access to the NDA'd vendor docs and the official SDKs. And, the vendor docs are bad and the official SDKs are a mess. Internal documentation? You'd be lucky if it's two steps above "nonexistent". It's usually just one step.
It's definitely better to not keep data locally if it's going to be seized, because of varying laws that can coerce unlocking, but in the U.S., it should be safe to refuse to give up passwords.
On the technical side, Google and Apple have changed the game with numerous improvements to physical security and GrapheneOS takes it even further building on their foundation reducing attack surface and adding good features. Particularly with Auto reboot[1] becoming widely adopted, your conclusion can be modified on phones.
[2]:
>This (https://osservatorionessuno.org/blog/2026/05/demystifying-ph...) is an article by an Italian non-profit that provides an introductive technical overview to forensic phone unlocking exploit kits used by governments and law enforcement, most notably Cellebrite.
>This post provides an overview on how disk encryption works on Android, common attack vectors used by forensic tools to brute force or extract a device, their countermeasures against popular security features like automatic reboot in iOS and how you can protect yourself against such tools, including several mentions about GrapheneOS.
[1] https://grapheneos.org/features#auto-reboot
[2] https://discuss.grapheneos.org/d/35728-demystifying-phone-un...
Just because a sufficiently advanced and determined attacker can own any device with physical access doesn’t mean we might as well make it easy for anyone.