You have to use the home address as the main point to send the postcard & list on the Google business page, then hide the address. Do not use virtual offices, po boxes, or anything else to try and game the system. The reason Google is tougher on this niche is because so many locksmiths have done shady things to manipulate the system and gain an advantage. Follow the rules and set up the page legitimately to have longer term success.
If there is no physical office location, you must use the home address. Optimize the website to cover the different service areas that you want to target (use local landing pages), which will help improve organic ranking in those areas. Do not create multiple pages for each location (that's another violation), just use the home address & hide it on maps when you select a service area.