My license(s) said, "Low Voltage Communications." I think one of them is still current. I did alarm, phone, video, intercom, sound (pro, res, and commercial), access control, environmental monitoring, TVRO, networking... Oh geez. I could fill a page with the different types of jobs we did. Along with quite a number of jobs that fell under the category "supplemental trades." I was running a PC service business out of my house in 1993, delivering pizza on the weekends, and was the shipping and receiving clerk for Tool and Supply during the week when my first contracting customer called me. I actually told them I didn't want the job at first. When I quit contracting on December 31st 2016 that customer was still with me. I called them personally and asked them to give the company that was buying out my accounts a fair chance.
I had customers who would call me and say, "We have an (XYZ System) giving us problems. Can you fix it?" It was rare that I couldn't and then usually only if the mfg had proprietary distribution. Often I could even then unless they needed OEM parts. Even then sometimes I had connections. Often I learned a system while I was troubleshooting it for less total (and charging more per hour) then the guy who came before me and didn't fix it. Yeah I am bragging a bit, but I enjoyed being a technician and trouble shooting problems. I just didn't care for how the contracting business changed after the depression that started with the real estate crash the end of 2005. I was still making money, but you had to be hard nosed with everybody. I didn't like that at all. I just wanted to be a technician and fix stuff. By 2012 I found I sometimes had to square off nose to nose with general contractors in order to be treated fairly. It was a fight. (Usually not physical. LOL) I can fight, but I don't enjoy it. I enjoyed being a technician.
To be totally fair. I probably did my very first paid machining project for a job I did for the Justice department in about 95 or 96. I made a press die for recessing photo sensors mounted in metal plates so people walking by wouldn't abrade the lenses when they brushed up against them going through the border crossing turnstiles. It was for a people counting system I designed. Well I didn't design the components. Just the system. Yes, I was a listed GSA contractor for a number of years. Did work for Justice, Marine and Airforce contractors, and directly for the Army.