The most basic difference between a monitored and an unmonitored home alarm system comes down to one thing: who is alerted in the event of a break in. Home security alarm systems that are not monitored send out signals to the home owner, and the neighbors while systems that are monitored, send additional signals out to the security company and local law enforcement.
The Pros and Cons:
Non-monitored systems generally are, or can be, do-it-yourself type projects. While as, monitored systems usually need to be installed by the security company of your choice.
Monitored systems tend to come with a monthly fee, meaning there is an additional expense throughout the year.
Non-monitored systems need more follow through. In the event of a break in, either the homeowners or the neighbors will have to react to the situation. If a thief stays in the home for a prolonged amount of time, it may pose a threat to neighbors and the homeowner, if the police are not called right away. With a non-monitored system, you risk the chance of responding too late to an emergency.