Final answer:
Out of the options provided, the one that is not a peace officer is the firefighter, as they are primarily responsible for responding to fires and emergencies, not enforcing the law.
Step-by-step explanation:
The peace officer is a term generally used to describe anyone invested with police powers to enforce laws and maintain public order; this includes police officers and sheriffs. Firefighters, while they do serve the public and respond to emergencies, do not have these police powers and are therefore not considered peace officers. Security guards also may not always be considered peace officers as their powers are usually restricted to the property they are hired to protect and they may not have the authority to enforce laws beyond their jurisdiction unless they have gone through certain certifications or are also sworn in as special police officers.