This has been discussed at length many times, but I just read an article that had a couple of gems I have not seen worded this way before:
Training with your firearm for months can make you seconds faster, putting a security plan together takes much less time, but can give you minutes of advantage.
In addition to retreating to the barricade/safe room, locking the door, announcing you have a gun, and calling 911, they suggested hitting the panic button on your car.
I honestly had not thought about hitting the car alarm. This would also be handy if you see someone sneaking around outside your house, even better if they are sneaking around your car.