How Effective Are Car Alarms?

Many people argue that car alarms are no longer effective. Car insurance companies and law enforcement agencies have both completed studies that reveal car alarms do not noticeably reduce car theft.

In fact, the SA Police Department has gone even further, declaring that car alarms are increasing crime, rather than reducing it, due to the growing number of call outs in relation to complaints about faulty alarms.
The reason is that car alarms are so sensitive that they are usually triggered accidentally, with the result that people have become immune to them, ignoring them as false alarms.

Their tendency to go off accidentally can be the result of overly sensitive settings or incorrect installation. Having your alarm professionally installed and set to a level where street noises and small vibrations will not set it off can reduce the problem.
Car alarms are somewhat effective against amateur thieves and joy riders, as they will usually select a car without an alarm before one that is alarmed. Professional car thieves, however, can disable an alarm in just a few seconds. Car theft is now an $8.2 billion a year business in the U.S.

Ineffective car alarms cause noise pollution and stress, waste police resources and do not get a second glance from passers-by. So perhaps the question should not be how effective are car alarms, but how can we make them more effective?
There are a growing number of alternatives to an audible alarm. Many car manufacturers are now installing immobilisers rather than alarms in their vehicles. Immobilisers are silent but effective, rendering the car un driveable. If a car with an immobiliser is stolen, it is generally because the thief has gained access to the owner's key.