We just moved into a house with an existing alarm system and contacted all the big name home security companies to find out about getting it monitored. All of them said they couldn't use any of the existing sensors, and that we'd have to switch to their system (for a huge fee, of course). Not only that, but if we wanted to have a cellular connection, or be able to arm the system from our phones, there was an extra monthly fee.
After many frustrating phone calls, we stumbled upon True Protection, and the whole process couldn't have been easier. John came over to the house to check out the existing system and explain everything to me in person, he even showed me the app on his phone that controls his own personal alarm system and home automation!
Of course, we scheduled the installation straight away and John came back personally to upgrade the control panel, hook up the existing sensors, and add a motion detector.
I've already recommended True Protection to a friend, and I'll definitely be calling them when it's time to add home automation.