One cannot discount the fact that there is always a threat of intrusion to ones properties. That intrusion could be very dangerous as ones property can be emptied in no time incurring great losses. Theft may include furniture, equipments and other valuable items, including cash that may be present at that time whether in a vault or not. Don't discount that secrets may be stolen too such as theft of some personal tapes or CDs or even a desktop computer or a laptop that may contain valuable and confidential matters like passwords, security numbers and the like. Don't discount too the most bitter thing that can happen and that could be an attack on lives. One of the best home security devices utilized these days is the use of burglar alarm systems. There are the mechanical types or the electrical/electronic ones or both; but, in most cases, a burglar alarm system refers to the electrical/electronic type.

*Info taken from http://ezinearticles.com/?Why-Home-Security-Devices-Are-a-Wise-Investment&id=2545285