Your best security device is your neighbors. Arrangements should be made with your neighbors to report any person or condition which is not consistent with the neighborhood. Statistics show that in neighborhoods where residents are concerned with their mutual safety, crime rates are lower. Advise your neighbors when you will be gone for an extended period of time. When valet parking your car, or leaving it for service, remove the other keys from your key ring.
Burglars have been know to duplicate house keys.
If you return home and find a door or window unexpectedly open or ajar, don't go in. Go to your nearest neighbor and contact the police. If possible, watch from a distance and keep the police dispatcher informed of any activity that you observe. Often a burglar will drive or walk through a subdivision looking for a home that appears unoccupied. This can be determined by clues such as an open garage without cars, an accumulation of mail or newspapers or notes stuck on the door.