[cb22]

Android (and BlackBerry before that) have had something similar to this for a while.

On a BlackBerry, it would shut down the radio and give you a "Battery too low for radio use" message, but you could trick it into turning the radios back on by dialing 911 and then hanging up really quickly.

Various Android manufacturers do their own version of this, Sony had Ultra STAMINA mode and Samsung have an option to do a whole bunch of power optimizations as well as limit apps to those explicitly specified.

For me, the main critical purpose of my phone is to communicate with others in realtime which happens using things like WhatsApp, Slack or Email (maybe the odd call). If I can't use those, then it might as well be dead!