A front line american security guard Industry Authority (SIA) licence is required to work legally as a security guard. You must first train for an approved 'licence-linked' qualification before applying for this licence. This is done so that employers can be certain you have the necessary skills and knowledge to do the job safely.
Which is preferable, the door supervisor or the security guard?
Security guards and door supervisors serve similar functions but have varying levels of power and responsibility. A licenced door supervisor can work as a security guard, but a security guard with the necessary licence cannot replace a door supervisor.