We route all of our 911 calls to Security first and then Security makes the determination whether or not to conference in 911. We don't want the police/emergency vehicles showing up without knowing what is going on and where to send them. We also have backdoor access to 911 that a few KEY people know about.
It helps that we have trained first responders that can be on the scene in under 2 minutes, 24 hours a day, anywhere on the complex.
If all else fails, almost everyone has a cell phone.
YMMV.