Sorry to hear about your accident, glad you are ok and the car is not badly damaged.
The hazards came on because the crash sensor detected a collision of enough severity to activate them. The doors should have also unlocked automatically and interior lights turned on.
The restraint system warning is due to your seat-belt pretensioner and/or anti-whiplash active head restraint deployment. When that happens they need to be replaced. If your head restraint doesn't look any different it was probably the pretensioner.
It's not tied to airbag deployment. The emergency systems trigger based on the measured severity of the collision. So it may turn on the hazards and unlock the doors but not trigger the battery disconnect or any airbags. However, an airbag deployment will usually trigger everything else including the BMW Assist emergency call.
Good information. After looking more closely, it is the anti-whiplash system. The headrest on the drivers seat is noticeably different than the one on the passenger side.
My neck was sore for about 24 hours, but is OK now. I'll probably go to my chiropractor in a day or two just to get checked over/straightened out.
The amount of safety equipment in these cars is pretty amazing.
After the wreck, the interior lights came on, the flashers came on and the doors unlocked after about a second or two. I also immediately got a restraint system failure warning - related to the anti-whiplash system. (I assume)
None of the airbags went off.
We called AZ DPS immediately and everyone had insurance (amazingly). All of us were wearing our seat belts, and noone tried to hit and run. I should have gone and bought a lottery ticket afterward. DPS has computers and printers in their cars, so the officer gave each of us a copy that summarized everyone's information.
The interesting thing is that the morning after the wreck, I was caught in that tanker truck mess here in Phoenix that made the national news. They closed the freeway (both directions) plus the interchange from another major freeway. It took me over an hour to move to the exit and get off the freeway.
I drove the car home afterward. I'm arranging for a tow truck to take it to the body shop for repair. Penske owns a bunch of high end dealerships _ Porsche, Lamborghini, Land Rover, BMW, etc. and the also a body shop that these dealerships send their cars to. So I am having it towed there.