When we recently moved into our new house, my wife was concerned about the main floor windows and the possibility of someone entering through them. Despite my reassurances that our dog would take care of any intruders (he wouldn't), she still wanted me to research and purchase an alarm system. Determined to integrate this future alarm with our existing home automation, I had a laundry list of criteria for the system and I wasn't sure I could find something that would meet my needs without significant modifications or hacks.
I began by looking at standard alarm systems from the likes of DSC, GE and Honeywell as well as serial interfaces for the computer. On one hand, these alarm systems are plentiful and cheap however they also require significant custom software rules to handle the interface, and most of the systems (like the DSC Power864) didn't allow access to the sensor inputs directly, so you'd know the basic alarm state, but not much more. Then there's also the requirement to have a dedicated computer running 24/7 and hope that the OS stays stable for months on end.
At this point it was looking like I would have my work cut out for me. As I continued to investigate things, I stumbled upon mention of the Elk M1, which sounded more like a controller (such as the ISY-99i) than a security system - The Elk could handle complex logic chains and had almost every input and output option imaginable. The system firmware is upgradeable - heck, the keypad firmware is upgradeable. There are keypads, temperature sensors, two-way speakers for listening remotely, thermostat integrations, serial and ethernet outputs, proximity readers as well as the full 'standard' alarm stuff like phone line monitoring and battery backup.
Did I mention the system has a 500+ word vocabulary and can speak the status of any events to you? Or that it can call your cell phone while you're out (up to 8 different numbers actually) and tell you exactly what's going on? Yea, it's those sorts of things that pushed me over the edge…I had to have it.
In order for me to integrate with my home automation setup, I figured I could use the ethernet output and have the ISY-99 control things from there. It turns out it's simpler than that, you can get a direct integration for almost all the home automation manufacturers (HAI, RCS, Aprilaire, OnQ ALC, Centralite, X10, Z-Wave, UPB, Creston, AMX and the one I cared about: Insteon) so the system can directly read and control devices. Some will still prefer to use an ISY or software to control things - and you certainly can - but it's not necessary with the Elk M1 as it would be otherwise.
For monitoring the system, we haven't decided on a provider yet, or if we'll get one at all (having the system call us would allow us to call the police if necessary) but any experiences with good and bad providers are welcomed. The Elk does qualify for home insurance rate discounts as well - Our discount wasn't that much of a drop, but it helps with the overall cost of the system (or my mental justification of it anyway).
There are a few places that sell the Elk, but these guys have it consistently cheaper than anywhere else I found.