Douglas is the principal author of the Code Check series of field guides to building codes and Electrical Inspection of Existing Dwellings. He began working with Code Check in 1998, when founder Redwood Kardon asked him to assist in editing the first edition of Code Check Electrical. As Redwood moved closer to retirement, Douglas eventually moved into the principal authorship role for the series.
Douglas is a licensed general contractor and holds numerous inspection certifications. For several years, he taught residential and commercial electrical codes at the College of San Mateo. He is a principle member on the technical committee for Electrical Systems Maintenance of the National Fire Protection Association. From 2013 to 2019, he worked for the City of Santa Clara, where he was the supervising MEP (mechanical, electrical, plumbing) plans examiner and inspection supervisor. He has authored dozens of magazine articles and books. He has served as an expert witness in cases involving contractor and inspector standard of care, building codes, and construction defects, and been certified as an expert in Superior Courts in several counties. He provides seminars around the country to inspectors, building departments, and electricians on building and electrical codes, construction defects, and inspection techniques.