In CA, a security guard license ("Guard Card") is required for all security guards/officers in the state. In-house and contract guards must all possess this certification to work. More information...
Many places will hire you to work as a security guard without any certification but, often they do have at least a bit of training that they will give you after you are hired.
Depends on the definition of unarmed. Sometimes they can carry a taser, and sometimes they can't. At the very least, they have a pair of handcuffs and a radio