Or to add to the fear factor. "Look what I can do. I can enter your house, take and do what I want." And then hope OP would be happy to get her keys back and think all was well.
OP--I hope you find out more about how the fire was started. Ask questions. You are smart to get a few quotes for security measures and honestly, I would probably not hire the neighbor. I hope that this person, whoever it is, gets found or just gets bored and goes away. It's horrible when, what should be your safe space/sanctuary, becomes a place to be unsettled/afraid.
As to the posters who are STILL asking, "How did they get in to take the keys if the front door was locked? Why didn't the dogs bark?"
They had numerous contractors and subcontractors at the house during the renovation from the house fire. Any one of them could have developed a fixation on the family, made a copy of the key and come back and taken the keys to scare the homeowners. Or someone else got a hold of the code and took the key and made copies. Lots of possibilities. The OP and the dogs were in the back garden and heard/saw nothing until OP went to get her keys.
Whatever PP on here that made comments to the OP about her mental health? Next time, try actually READING the thread instead of sitting on the edge of your seat waiting to be witty, or have someone read the thread to you. First of all, it wasn't witty, it was lame, mean and quite unintelligent. Second point; the whole family has been a victim of the knocking and rattling, so your point wasn't a point; just a pathetic attempt to be noticed.