Over spring break I'll be taking a trip to the bay area and I plan on doing some exploring while I'm there.

I'm from Iowa and out here there is practically no security in most places. Only a few times have places been locked and the guards are either not there or not paying attention. My question is, how strong is security out there, especially East Bay? Are the guards more attentive due to higher populations and higher crime rates?

Most drains and tunnels don't have any security, you can go there without too much trouble.
The majority of abandoned sites with multiple buildings have security on site, but it's still possible to get in if you are patient.
Finally if you are into rooftops, most of the skyscrapers in downtown SF have security, either as roof door alarms, motion detectors, private security guards doing rounds (in hotels), or simply a security guy in the lobby who will let only residents pass (in residential buildings). A large number of high-rise construction sites also have cameras and/or guards. It's still possible to find nice rooftops, it just needs patience and multiple trials.

Most locations in the East Bay not deep in the hills should be assumed have at least periodic security patrols. Since space is at a premium in this area, most abandonments don't last long either, and those that are there are well known and usually have some issues (or combinations of them), such as being controlled by the Federal government, being in high-crime areas, or being traps from bored police officers.

Easy explores are bunkers lining along the coastline or islands like Angel Island and Alcatraz. There's also a decent ghost town in the South Bay near where I live.