system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can a completely deactivated phone with no wifi connection still call 911?
gpt
911 gets special consideration by the carriers due to FCC regulations.  This means a couple of unique things for 911 calls.  

First, even if the phone does not have a service plan attached to it, it can still call 911.  No service/no bill, doesn't matter, your phone is still allowed to make 911 calls.  Keep in mind though, that since your no-service phone doesn't have a phone number attached to it, if you get disconnected the 911 operator cannot call you back. 

Second, no bars doesn't necessarily mean you can't call 911.  For most numbers your phone has a minimum threshold of signal required for it to even attempt to make a call.  If the signal is less than what would represent 1 bar on the phone's display, the phone won't try a call because it knows that it's likely to fail/cause a bad experience for you.  For 911 though that rule does not apply.  Your phone could have 1 of 10th of 1 bar worth of signal, and it will still try and call 911.