If you want to make a career in security industry, you should have a proper license and certification to be able to find employment. In today's age of uncertainty and terror, security personnel are on an increased demand. To cash in on this demand, honest and people with integrity can look forward to a good and successful career in securing various areas.
For more details on the security industry and in particular door supervision I can suggest link and associated text pimping the link deleted. No advertising. If people want to get their SIA, a simple search will bring up a selection of companies offering SIA training, from which they can choose at their leisure

I work in the security industry and spent a few years working as a doorman (doorwoman?) in a busy club district. I enjoyed the heck out of it and consider it valuable experience on my resume. So do industry recruiters, and that has paid off for me financially. Why? Working in such a fast-paced environment where situations can develop at light speed really sharpens your focus and ability to maintain that focus for long period of time. Greeting patrons at the door is great practice in sizing up people and spotting possible trouble. Keeping tabs on the crowd teaches you how to spot breaks in the traffic pattern and step in with a team while the fight is still developing. And, of course, a crash course in police relations.