Alarms are a preventative measure, not a cure.

The most important part of any home security system is the burglar alarm. In its most basic form, a burglar alarm is a sensor that detects when someone enters your home, and then takes action – this action could be making a loud noise, calling the police, making valuables safes inoperable, and all sorts of other things besides.
Burglar alarms are generally hard-wired into the walls of a home, so that they can’t be easily disabled or removed, and any tampering with them will instantly set off the alarm. The mechanisms used to activate and deactivate them vary widely, from the more common keys and PINs to high-tech fingerprint systems.
Unfortunately, people are often mis-sold far more advanced home security systems than they actually need: a salesman can play on people’s fear of crime to sell them the very latest, computer-controlled alarm, complete with expensive expert installation and a monthly subscription to a 24-hour monitoring centre. This is a lucrative business, but is also amazingly unnecessary.
The dirty little secret of burglar alarms is that it’s not the features of the alarm itself that make the difference. Burglars don’t want to get caught by alarms, and so will avoid any houses with alarm boxes on the outside – it’s not worth the trouble for them to try. It’s a preventative measure, not a cure.
With this in mind, instead of spending lots of money on a burglar alarm, many people prefer to just fit a fake alarm box to the front of their house and be done with it. This puts off burglars by making it look like you have an alarm system, but avoids all the hassles and expense of actually having one. If you do this, though, it is important to make sure that the alarm box looks realistic enough to fool an experienced burglar, and also that you keep it a secret. If you go around telling everyone about your fake alarm – especially people who come to your door – then it’s worse than useless.