Research suggests that an audible alarm is less effective than car recovery devices, such as OnStar, and immobilizers when protecting your vehicle against robbery.
The quick answer: no. After surveying insurance claims for 73 million vehicles in 1997, the nonprofit Highway Loss Data Institute  found “no overall reduction in theft losses” for cars with traditional audible alarms. That’s because blaring alarms rarely indicate theft. So frequent are false alarms that people are conditioned to ignore them. Experts have concluded that as many as 99 of every 100 alarms switch on for reasons other than break-ins. In 1992, the New York State Legislature estimated that 95 percent were triggered by stimuli such as vibrations from passing trucks.
So it’s no surprise that fewer than 1 percent of people who hear a car alarm bother to alert the police, according to one insurance company survey—or that many more call to complain about the alarm itself.
Another reason audible alarms prove futile is that professionals account for 80 percent of car thefts; many can disable a standard alarm in less than a minute.
The bottom line is that leading insurance companies, including AAA, offer no discounts on premiums for vehicles with audible alarms. Many cars come with an immobilizer, a device that prevents the engine from starting unless it detects a computer chip in your key fob. It isn’t foolproof and it won’t get you a discount, but it’s harder to crack than a standard alarm—and it won’t wake the neighbors every time a garbage truck rumbles past.
This article was first published in November 2011. Some facts may have aged gracelessly. Please call ahead to verify information.