First and foremost consider the plain fact that a home without a home security system is statistically more likely to be broken into. The simple presence of the system acts as a primary deterrent. If undeterred however, the act of a person accessing the property will set off a deafening alarm, which has a dual role.
Firstly the volume of the alarm makes staying within the property itself almost unbearable, and secondly once an alarm is activated the burglar knows that somewhere, somehow a system is being activated that will result in the property being checked. By connecting your home security system straight to the police, you can receive direct intervention if you do not deactivate the alarm yourself with a code. Owning a home security system can also help in bringing down property insurance costs, which can be a welcome saving. It really does make sense to install one.