I've found iPhones way too fickle to trust them to stay off. If you plug in a charger or tap the power button they power back on. If you don't want to be tracked turn off your phone and put it in a faraday bag.
I would expect tapping the power button would turn most devices with a power button on. With respect to charging it, for most users that's probably the correct behavior. There are 2 reasons people seem to turn off (not just airplane mode or disabling some things) their phones:
1. To preserve a low battery or because the battery has died.
2. To fully disable the device.
(1) is by far the most common of the two. In that case, once it's charging then turning back on automatically is the desired behavior. In the case of (2), if you have a strong motivation (avoiding detection, for instance) then you'd presumably have done a bit of research or noticed that this happens and make deliberate choices around how you use and charge the device.
> I would expect tapping the power button would turn most devices with a power button on.
I believe I was thinking of my older phone. Tapping the home button, perhaps even the volume buttons, would turn it back on. On my Xs, I have to hold down the power button for a few seconds before it would turn on. I find this a bit more reliable if I want my phone to be off for awhile.
