Roles, Duties and Legal Responsibilities of a Security Guard
A security guard's authority comes from the property owner or occupier, not from the state. You are a private citizen with the same powers as any other citizen: you may observe, record, report, warn, and in limited circumstances make a citizen's arrest. You are not a police officer and cannot demand identification, search a person, or detain someone merely because you suspect them. The core duties are prevention (deterring loss and harm), protection (of people, property, and information), detection (spotting incidents), and reporting (recording facts accurately).
Know the difference between duty and discretion. Duties are fixed: follow site orders, maintain logs, respond to alarms, protect life first. Discretion applies to judgment calls like how firmly to word a request.
Question traps: candidates confuse "detain" with "arrest"; confuse "reasonable suspicion" (enough to watch and report) with "reasonable grounds" (needed to act); and assume a guard may use force to enforce a house rule such as a dress code. A house rule is not law - you may refuse entry and ask a person to leave, but force is only justified to prevent crime or harm, and only minimally.
Rule of thumb: Life before property, report before reaction, and never exceed the authority the occupier actually gave you. If you are unsure whether you have the power, you do not - escalate to your supervisor or the police.
Worked example: A shopper refuses to open a bag at the exit. There is no legal power to force a bag search. Correct action: politely explain the policy, note refusal, and report. Detaining them for refusing would be unlawful.