(MONEY Magazine) – Even as burglary rates have dropped to their lowest level in 30 years, Americans continue to spend more than ever on home-security systems. And after all, for the typical homeowner, it seems a simple equation: A sign in front plus contacts on windows plus motion sensors throughout equals a secure house. Besides, with the insurance breaks, many buyers figure such a system will practically pay for itself. So it's a no-brainer.

Or is it? Nothing about these security systems is as simple as you might assume. They can be expensive to install and to maintain--generally much more expensive than any reductions in your insurance premiums (see the box on page 130). Even when used properly, security systems are not fail-safe deterrents. There may be cheaper and more effective ways to ward off or trip up criminals. We arrived at this surprising conclusion after taking a hard look at security--a look that included seeking out a point of view generally excluded: that of burglars.

THE PERP'S-EYE VIEW

Enter Scott Decker and Dietrich Smith. Decker is the department chair of criminology at the University of Missouri-St. Louis and the co-author of Burglars on the Job: Streetlife and Residential Break-Ins (Northeastern University Press).

Seven years ago, after a lecture on the miscreant mind-set, a colleague of his was approached by a wheelchair-bound student who said: "That's not exactly accurate." That student was Dietrich Smith, who had grown up in one of St. Louis' roughest neighborhoods and had firsthand knowledge of plenty of illicit activity. At 23, Smith himself had been the victim of a gun attack that inspired him to clean up his act. Now he helps Decker supplement academic theory with street-level reality. Specifically, they study "active" residential burglars.

The research takes them all over the city, from low-income neighborhoods teeming with security signs, past storefront churches sprinkled among row houses of red brick fired from Mississippi River clay and, finally, to some of the finest homes that suburban St. Louis has to offer.

While the pair refuse to give their perpetrator subjects access to journalists, Decker and Smith agreed to take me along for a day's ride. Sometimes it felt like living an episode of Cops: On Cass Avenue, we watched police chase the fleeing passenger of a stopped car around an old Victorian while the driver was questioned. And then there are the stories, like the one about the burglar who used a narrow gangway to "Spiderman" his way up the sides of two closely built homes. Or the one about the barbecue where a "neighbor" took leave and proceeded to clean out everyone else's house.

But Decker and Smith's commentary is more than just colorful anecdotes. They have learned a thing or two that a home-security salesman might leave out. To be sure, Decker concedes, "home-security devices will work against some types of people." They are not universal deterrents, however. "Based on our research with residential burglars, these devices are of less consequence," Decker says. That's because burglars have told him that even if there's an alarm, they figure they have three to five minutes before the police arrive--and that may be all the time the burglars need.

Moreover, burglars may look to other cues to conclude that you aren't home, and they may know from experience that a sign in the yard might mean the owner has been lulled into a false sense of security and might not even have activated the alarm that day. In fact, a 1994-95 study by Temple University economist Simon Hakim found that in burglarized homes with alarm systems, 41% were not activated. Obviously, notes Decker, "the best system doesn't do any good if you don't use it."

Finally, he says, there's one more thing that the sign in front may be saying to a burglar about your house: "It must have something worth stealing."

YOUR MOVES

Again, all of this doesn't mean that a home-security system can't help, just that it isn't a panacea. And any number of smart--and cheap--measures may be equally effective. So think about the question from the burglar's point of view. "Often," says Decker, "little things tip the balance for someone who's looking for a place to rob."

Keep-away tactics. Probably the key issue for a burglar is figuring out whether you're home or not. So if you're leaving town, stop newspaper delivery, ask a neighbor or friend to pick up mail and arrange to have someone take care of your lawn. That's pretty straightforward stuff.

But remember, a burglar doesn't need you to be gone for weeks--a few minutes will do. In fact, most burglaries take place during daylight hours when residents are likely at work. As he tools through St. Louis, Decker points out open garage doors as a particularly obvious sign that a homeowner has stepped out. Drawn blinds on a quiet, unlit house can also be a giveaway. He recommends using timers for lights and maybe even the stereo; lights that never go off spell an empty house.

Your home is even more likely to be targeted if you leave tools around that will make a burglar's life easier: Ladders, for instance (yours or a neighbor's), can offer easy access to the second floor, where windows may not be secured or the alarm may not be wired.

Decker and Smith pull up in front of a recently burglarized ranch house in a middle-class suburban neighborhood. "Where'd he get in?" Decker asks. "The rear," says Smith. A burglar can guess that a back door might be less secure. In this case, the high shrubs may also have caught his attention: They're an easy hiding place if someone comes home. Interior obstacles. Once a burglar is inside, says Decker, "The bedroom is usually the first place they go." Why? Because that's where jewelry and other valuables are most often kept. So Decker recommends that they be stored in bathrooms, kitchens (not the cookie jar) or kids' rooms instead.

Basically, anything that prolongs a burglar's search is in your favor. "The more obstacles, the more you'll put them off," Decker notes. Dogs, he adds, are particularly effective. Smith laughs. He considers Help, his 100-pound German shepherd, to be his best deterrent. Smith, paralyzed from the waist down since the shooting, calls Help his backbone and says he got the dog because so many burglars told him a dog causes problems. "Especially," he adds, "if he's a 100-pounder."

Extra protection. With or without a security system, there are ways that you can fortify your house for relatively little expense. For starters, replace locks when moving into a home that's been occupied. Install dead bolts on all exterior doors, and make sure lock receptacles (held in place with two-inch screws) were not hastily repaired after a previous break-in.

Next, consider double-pane windows (which make burglars work twice as hard) and solid-core doors (which are more difficult to kick in or otherwise break through). Finally, motion-sensing outdoor lights that turn on when approached can fool a burglar into thinking he's been spotted.

WORKING THE SYSTEMS

Decker, incidentally, has no alarm system at his home. He's comfortable with dead bolts on all the outer doors, double-pane windows and a solid-steel door to his walk-in basement. But he concedes that, for some, security systems supply a feeling of extra safety and peace of mind. "If they get that," he says, "they aren't wasting money."

Unfortunately, this can make a buyer vulnerable to overpaying. So before you opt for the fanciest system available, security experts say, make sure you're getting one that's consistent with your lifestyle. Complicated motion sensors that have to be turned on and off every time someone leaves the house can be a nightmare if you have kids coming in and out, for example. Supersensitive systems are also prone to false alarms--which make up 94% of all security-system activations. (That shockingly high figure causes other problems: Many cities now levy fines for false alarms. In Boston, for instance, the first two false alarms are free, then it's $50, $100 and finally $200 for each subsequent cry of wolf.)

It's also critical to select the right alarm company. Many of these businesses, says Temple economist Hakim, are "fly-by-night installers just looking to get a monthly check." For recommendations, talk to your insurance agent or friends who have systems. Companies registered with the National Burglar and Fire Alarm Association (www.alarm.org; 301-907-3202) are required to conform to an industry service code. "You really want to have detailed conversations with the company you choose," adds the NBFAA's Dave Saddler.

Our tour, meanwhile, ends on Smith's old block. "These are my buildings," declares the self-described mayor of Lafayette Square. All around, he sees signs of locals who are heeding his advice. Everywhere, the blinds are open. "It really works," he says emphatically. Then, smiling, he gets in a last plug for the canine cause. "And there are dogs in that house, that house and that house."