Why? Is there any way to be certain these are done in hardware and can’t be caught in a low level system once the device is rooted? It’s a black box, so no way to know until somebody manages to pull it off.
If you suspect your device has been tampered with and need a guaranteed reboot, just let the battery run down and don't use it until it has.
Just a (overly paranoid) thought: a sophisticated attacker could simulate a drained battery and subsequent reboot, no?