Just tested it and can confirm it works. For those that don't have their phone handy or are worried about trying it:
- Just 5 presses is enough. You could do 6, or just spam the power button to make sure you've got at least 5 in. Any presses after the 5th don't do anything different
- when you do it, it opens up a menu with options to:
- Power off
- Make an emergency phone call to 911 (there is no option to select an emergency contact. It just calls 911 immediately)
- Show emergency medical info
- Afterwards, you need to enter in your pin/passcode to unlock your phone. I have Face ID and the ability to unlock my phone via my Apple Watch. Both methods are disabled until I unlock my phone with my code.