How do I build a side door into my garage
See if these help you.
What type of exterior do you have? Siding? Stucco? Brick or block?
I have listed a link that gives some very good instructions on how to do this.
here are videos https://www.youtube.com/results?search_query=DIY+add+sidedoor+to+garage
The first thing I would do is go to the City office and find out if you are allowed to do that, how to get a permit, with the information on who will be doing the work, and then 2nd, talk to your insurance agent---I am assuming you will want the alarm to work on that entrance as well.