The point isn’t to make it forensically undetectable, but to prevent the room temperature IQ cop from noticing what happened. If they “unlock” the phone and don’t see anything that looks out of the ordinary they won’t make a big deal out of it and there’s a chance they’ll let you go.

The room temperature IQ cop is going to plug the phone into a system that will do that forensic detection. Using commercial or special software.

Room temperature IQ cop knows how to plug the cord into the phone and the cord into the laptop.

@GrapheneOS

It would be trivially detected by widely distributed standard forensic software including the non-Premium variant of Cellebrite able to run on a laptop.

By "duress profile", I mean that if user has enabled a "duress profile" feature in Settings, then entering the duress PIN would:

1. Erase (the encryption key for) all profiles and storage outside the duress profile; then
2. Unlock the duress profile.

So, how would forensic software detect that the unlocked profile is a duress profile?