How do we know which devices are sentient? The first ones could have ran GM-NAA I/O for all I know.

Not how we'll know, how they'll know.

“i OS” also works, and they may process their thoughts in their own bodies instead of receiving them remotely.

Well, the first sentient device will probably be some supercomputer, so it won't be either of those. ;)

There is no rule that supercomputers cannot run on Android.

Let's just hope a new digital consciousness will be able to first observe something other than the Play Store or it's going have a very dim view of us.

No rule that I know of that sentience necessarily requires a supercomputer, either.

Coming from someone that thinks houseflies are most likely sentient at some level.