What if they thought you would do that and specifically took it to a police station that you did not have a geofence for? Mind you, they wouldn’t necessarily know. But it’s not impossible.
It also might not be taken to a police station. Who knows where the actual forensics labs are. No real need for them to be on-site or even labeled.
If you have the 10 seconds, you could use the operating system’s hard reboot function, which at least on Android is pressing and holding power and volume up for 10 seconds. But I don’t know what it is on the iPhone.
Power and volume up for new phones, and then power and home for older ones with Touch ID.
Also, so you know, if you press power 5 times it will ask if you want an emergency call, say no, but after you do it your PIN is required to unlock. No biometrics work at that point. So, no one can force you to touch or look at it. I don’t know if it puts the phone in that “mode” or not, but it’s a handy trick.
