PSA to iOS users: if you tap the lock button 5x it forces password-only unlocking. Useful at protests or any precarious situations with law enforcement.
This still leaves your device in an AFU (after first unlock) state, with user data decrypted, and should not be treated as secure.
The only thing you can do (to protect your data from forensics, etc) is to return it to BFU by shutting it off.
Bringing up the shutdown screen (hold lock and either volume button) will also do it.
On GrapheneOS (and maybe android generic?) this calls the emergency number, I just found out (with a 5 second timer to cancel this luckily)
- TSA: Hey, bring your bag and devices here. Routine inspection.
- Traveler: [takes phone from the bin] [finds lock button] [click] [click] [click]
- TSA: Hey, stop what you're doing Mr. Terrorist!