The biggest obstacle to tyranny is an informed public. Just look at the videos that have brought down senators (macaca, anyone?)
Many of us have cell phones now. They can be powerful tools for democracy.
First of all, for you and your family, emergency agencies recommend making an address book/contact entry for "ICE" (In Case of Emergency). This will help the "authorities" contact your loved ones.
Okay, that's worst case scenario. What about "lesser case scenario"?
I have all of my local news affiliates' numbers programmed into my phone.
This way, if I see abuse, or a tense protest, I can call the local news outlet and fill them in.
Use your phones to get the media involved!