It sounds like you’re thinking of working as an independent contractor, not necessarily starting a full-fledged business. Make sure you understand the difference and the responsibilities that come with each.
I’ve noticed some companies are offering remote guard services, where motion-detection cameras are monitored by staff off-site. That might be something to consider.
You should approach property managers. They often manage several businesses in one location and may be looking for security services.
One way businesses might justify paying for security is by considering it a deductible business expense. You should consult with an accountant or tax professional to get more details, as this could be a selling point for your services.
@Chen
Why comment if you don’t know what you’re talking about? Please do some research before posting advice.