I use DSC security hardware along with Travis' excellent
DSC Plugin and an
Evisalink. DSC can communicate with my monitoring service via landline, Internet, and cell call, alternatively. Monitoring services online are much more reasonably priced than what I had paid ADT / Brinks. Has worked extremely well for five years.
Purchased the DSC hardware and had it professionally installed. More $ upfront, but the installation was performed well (better than I would have). It allowed for installation of three different keypads, wired motion sensors, and a few extra sensors that I would n't have considered (but the pro did). The monitoring service reductions have more than paid for the installation and equipment costs at this point . All I have to do is change a couple batteries every four to five years.
Some of the nice integrations with Indigo include: Automatically locking doors when alarm is armed, sending me texts with the real name of any open window or door that is preventing alarm from arming (DSC panel provides a code number, but Indigo converts it to a real name, like Kid's bedroom window), provides me text notices of alarm events, automatically arms alarm in some circumstances, ....
Berkinet provided a separate plugin for other alarm systems, possibly Ademco. Someone else might provide their experience with that, but everything I've read over the years suggests that it's also an excellent option - making your hardware choice / preferences key.