There is an increased police presence at BART stations and the transit agency they're taking the initiative on their own in part because State Homeland Security officials have long identified the BART system as one of California's top 10 terror targets.
The BART Police Counter-Terror Team was formed with TSA grant money in January; since then, they've been training and preparing for a day like Monday.
"It was all put together over the evening. We all got called out last night that said, 'Hey, be to work tomorrow, we're going to be doing this' so here we are," said Sgt. Ed Alvarez, from BART's critical asset patrol.
The seven-member team was supposed to be at a two-day training session on current domestic and international terror groups. That was canceled. They're on the trains and platforms instead, with the help of another eight or so regular BART officers, watching for signs of a possible terror attack.
"I don't think you can ever fully be prepared. I think just [being] vigilant and people's help in being observant is going to be the best deterrent," said Alvarez. "Bottom line, if it's going to happen, it's going to happen, but we can try to deter it from happening."
"I think it's a good idea. I do because I think that there may be some people may be reacting," said Bliss Birchett from Fremont.
"I think if anything is going to happen, it'll be days or even months. I don't think anything's going to happen right away," said Kim Beavers from Oakland.
San Francisco police didn't add any officers, but gave those on the job specific instructions to keep an eye on transit and places of worship.
"This is a big event, I mean, this is something that's 10 years in the making. You don't know, there is sometimes people might think about retaliation," said Officer Troy Dangerfield.
The TSA says it will be business as usual at airports, with the same kinds of screenings we've come to expect, and perhaps dread, over the last 10 years.
A statement issued today reads, "TSA continually evaluates the latest threats and screening measures, which are implemented based on the latest intelligence."
Bay Area icon the Golden Gate Bridge says it's been on high-alert ever since those first hours after 9/11 and Osama bin Laden's death will do nothing to change that. Many of the bridge security measures are designed to be invisible to the public and they'll stay that way.
BART and the SFPD are acting on their own, as a precaution. They are not aware of any specific threats.