No, a CB won't work as a police/fire scanner. A handheld ham radio will, however. The channel 9 emergency button or switch is a little outdated now. However, if you go back a few years, a lot of the police, fire, and other emergency services used to always have a radio monitoring on channel 9. That was the CB channel you could go to if you "needed help". It's pretty much dead now, although there are probably a few services around the country that still monitor it.
If you want something that you can talk to others on & also scan for police/fire, you should look into ham radio. You do have to take a test, but it's pretty simple (and they give you the questions & answers ahead of time). Most handheld ham radios will be able to scan and monitor emergency frequencies, no problem.