These types of systems have been around for many many years. They are usually from ADT or an Internet service provider, or a cellular provider. The deal is you get the system for free, or at a quite low cost, but that you have to sign up for their service for 2 or more years. People don't like big up-front charges so this works for them. Obviously the system is not free, and they can make up the cost a little every month in the service charges, which cost you double what you would normally pay. After the two years, they have their money back for the "free" system, and the rest is pure profit.
So when when someone comes upon these systems and wants to have them monitored by someone else, guess what? Its not possible. At least not possible without lots and lots of work. So reuse any part you can, but likely its not very useful and you'll want to get a new system.