Mary Jane Coolen and Ed Terry think of their Cheverly neighborhood as a generally safe place to live, where neighbors know and look out for one another. But when they leave home, they always turn on their burglar alarm. "It gives us peace of mind," Coolen said, noting that they had it put in after a 1998 burglary.

Coolen and Terry are among the growing number of homeowners who are hiring companies to install burglar alarms, also referred to as electronic security systems, in their homes. In 1970, a negligible number of U.S. homes had such systems, according to research by J.P. Freeman Co., a Connecticut-based research, consulting and services firm. By 1979, they were in about 2 percent of homes. That figure rose to about 20 percent by 1992, and to 32 percent now.

Homeowners are not seeking security systems because of any widespread increase in burglaries. To the contrary, that type of crime has declined. According to the annual National Crime Victimization Survey conducted by the Bureau of Justice Statistics at the Justice Department, 29.8 of every 1,000 households were burglarized in 2003, compared with 58.2 per 1,000 households in 1993, 84 per 1,000 in 1983 and 110 per 1,000 in 1973. The survey defines household burglary as an "unlawful or forcible entry or attempted entry of a residence. The crime usually, but not always, involves theft."

Nor are homeowners buying security systems to increase the value of their homes at the time of resale, said Dale E. Mattison, an associate broker for Long & Foster Real Estate Inc. and a member of the board of the National Association of Realtors. He ranked burglar alarms much lower than central air and off-street parking on the list of amenities that home buyers want. "Maybe they are equivalent to or a step above outdoor speakers," he said.

Electronic security systems have grown in popularity in part because the cost of installation had decreased significantly in the past 15 years. In 1990, a home security system cost an average of $1,509, according to J.P. Freeman Co. research. By 1999, the average price had decreased to $1,000. Today, you can get one for about $95, said Joe P. Freeman, chief executive of J.P. Freeman Co. He noted that most companies require buyers to sign a monitoring contract that costs about $30 a month.

Also, many insurance companies offer discounts of 10 to 15 percent to homeowners with security systems.

Perhaps most significantly, security systems appeal to homeowners because when turned on and used properly, they are the most effective way to deter burglars, said Simon Hakim, a professor of economics at Temple University in Philadelphia.

In his research on home security since the early 1990s, Hakim has found that homes without security systems are about three times as likely to be broken into than homes equipped with such systems. Losses due to burglary average $400 more in homes without security systems than in homes with security systems, he said.

Alarm systems are highly effective because a burglary becomes "not worth it," to criminals, Freeman said. He said many burglars want to "smash and grab," and that a burglary is "a panicky attempt to get some wealth." When an alarm is on, the intruders have to get inside and either disarm the system or get in and out in about 45 seconds, both of which are more difficult than breaking into and entering a house without an alarm, Freeman said.

But crime experts say an electronic security system may not be enough to prevent a burglary because people often forget or deliberately don't turn it on when they leave home for work, errands or vacation -- when homes are most vulnerable.

"Alarms are only as good as we are at using them," said Jean F. O'Neil, director of research and evaluation at the District-based National Crime Prevention Council, a nonprofit education organization. Fifty-seven percent of burglaries in the United States in 2003 took place without forced entry, according to the Bureau of Justice Statistics. That means burglars often gain entry through unlocked doors or windows, or found "hidden" keys, O'Neil said. And alarms, even when turned on, are not foolproof.

It makes sense to take some practical precautionary measures, whether or not you have a burglar alarm, several experts said. "There's a lot you can do that doesn't set you back a huge amount," O'Neil said. Here are some suggestions:

* Inside, keep your doors, windows and garage locked at night and when you leave home. Secure windows with a keyed lock or pin, especially those on the first floor. Make sure exterior doors are made of solid wood or metal and secured with a deadbolt.

* Outside, cut bushes low so that burglars can't hide in them. Install motion-detecting lights. Leave a spare key with a neighbor rather than under a doormat or in a planter. "Burglars have more experience looking for keys than any of us have hiding them," O'Neil said. Place a sign in your yard that says your home is protected by a security system. In Hakim's studies, most homes with security systems that were burglarized didn't have a sign outside. Even if you don't have a security system, that kind of sign "can't hurt and the cost is negligible," said Todd Post, assistant director of communications at the National Crime Prevention Council.

* Make your house look lived in when you travel. That's what Joseph Stephenson always did when he left his Upper Marlboro home for a few days or longer. Stephenson, who now lives in a gated community at Leisure World in Silver Spring, used to cut his grass and hedges just before leaving. He put timers on each floor of his four-story house that turned lights on and off at appropriate times. He stopped his mail and newspapers if he was gone for more than two days. "I always felt better when I left the house more secure," by supplementing the alarm system that he had, Stephenson said.

* Join neighbors to look out for one another's homes. Start or join a local Neighborhood Watch Program, in which police teach people how to be on the lookout for crime and how to report it. Nationwide, more than 20 million people are involved in that program, O'Neil said.

It takes effort and costs money to make your home safer. But statistics show it can pay off if you can prevent your home from being burglarized. According to a 2003 Justice Department study, the tangible losses from an average burglary or attempted burglary cost about $1,500.

"Prevention is a whole lot easier" than paying the price once it happens, O'Neil said.