Thanks for all the responses guys!
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I completely agree that if you live somewhere near a city or a generally tough area, you lock up. Like BBreslin, my parents were always of the opinion that if they want to get in, they're gonna get in, so why risk them breaking the windows.
Meghan2828, I never knocked either. I always just walked into the home of whoever I was visiting if I knew them particularly well. Sometimes I might knock on the door as I'm opening it and walking in and people always did the same to us.
In this part of Shropshire, we always lock the doors. It was hard for me to get into the habit though, but there are lots of burglaries in the area, so I can understand why people are so concerned about locking the doors.
When I'm in, the windows are wide open and the front door isn't locked. I just make sure that anything valuable on the ground floor is out of reach from windows and out of sight as well.
Anyway, regarding the car theft on my estate, a man knocked on the door of one of my neighbors the other day. The neighbor answered and the caller asked him if he knew someone by the name of "Mr. X." The neighbor said no and the caller left. The following night, there was a break in while everyone was asleep upstairs and they made off with a tv and their laptops. They also took the keys to all the cars. They used one set to move the ford focus that blocking a new Audi in and then stole the Audi. So, it's believed the man asking for "Mr. X" was calling to figure out the best way to rob the house. So, be careful everyone!