Starships aren't military vessels... but security is important... and I'd imagine it would be akin to personnel being expected to behave themselves responsibly (so monitoring of the crew isn't really needed), but crucial areas would be under constant surveillance. If a problem of some kind occurs, then the said security systems would need to be circumvented by technologically knowledgeable individual and/or external force. There ARE ways to write around the problem and still retain the technology in question... or at the very least lead the crew to what happened (in the case of an external force and brain monitoring technology, it would be possible to determine whether the person acted on their own, or were compelled by an outside force). You also don't need to deal overtly with the technical aspect. When Lon Suder murdered his fellow colleague on night duty in engineering, the Doctor discovered from the autopsy fairly quickly that it was indeed a murder. The rest of the episode was about how to deal with Suder's violent tendencies and the effect they had on Tuvok when he mind-melded with him. Suder however was a special case seeing how he was a Maqui with violent tendencies. But how many episodes did we have on any given series on a Federation ship with the crew itself causing issues out of the blue? Not many... and even then, there was an external force at play.