The key to successful home security is layering. Bear in mind, this doesn't mean piling gadget upon gadget. To decide how much protection is enough, Thomas Davidson, coauthor of The Complete Idiot's Guide to Home Security (Alpha Books, $12, www.amazon.com), suggests asking these three questions:

1. How likely is a given threat? Has there been a rash of burglaries in the neighborhood? Or do most folks in your town not even lock their doors?

2. How big a problem would it be if it happened? If thieves broke into your house, would you lose priceless artwork or expensive electronics?

3. How difficult or costly would it be to eliminate the risk? An alarm system, for example, can cost $1,000 and up. If you've implemented basic security measures — ensuring all points of entry to your house are well-locked — and still feel further precautions are warranted (because, say, crime is rampant in your neighborhood, or you have possessions of exceptional value), consider secondary measures, such as alarm systems or surveillance cameras.