I want to turn on audio or video recording in a way that is not reversible.

Being able to start the camera without unlocking the phone is a good step, but you can also delete the footage just recorded if someone apprehends your device. I would be interested in the option to not be able to delete that footage.

I would also be interested in being able to live-broadcast (maybe just audio?) to someone else's device to prevent the evidence from being destroyed also without having to unlock your phone.

Good idea. I wonder if it exists in their emergency app if not it should.