After several thefts in my house over the course of 4 years (I was single at the time no one home during the day). The Police said to get a dog. They are a good deterent as they make a lot of noise; otherwise there is just about 0 chance anyone will notice.
I did not want a dog so I put bars on my windows and bought an old style wire type alarm system from Radio Shack (thats my dog to make noise). I most of and my best tools inside of the house in a large closet in the middle of my house. I has a regular door that I reinforced with iron strap metal and the hinges are such that they cannot be pried off with out tearing the wall apart. It has a Dead Bolt Lock and A security type Pad lock and the part that serves as the hasp is welded to metal frames. It is also hooked up to the alarm system.
In past thefts when the Police came to my house the first thing that they ask was "who was here last" indicating that most often thefts are done or the information relayed by someone who knows you.
I think we all no someone who while working on some project who has a garage that faces the street and leaves that garage door wide open for any one to see all of their goodies inside.
Since I put up the bars no one has tried to get in. Before that time I would sometimes come home and find someone had taken off or pried on my screens attempting to get in and for whatever reason they changed their minds.

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84 300D, 82 Volvo 244Gl Diesel