Here are some very good home security tips from the Houston area. The specific details start about half way through. Follow the link at the bottom:
"One of the issues discussed was the use of locks. Traditional door locks located on door knob have spring locks, which are easy to open with a credit card. Krysiak recommends a single deadbolt for doors without windows and a double deadbolt for those within 40 inches of a window. A double deadbolt is one with a lock on the inside of the house. The bolt should be at least an inch long."