we have one through a private company--it covers the doors, the sheds outside, no motion detectors (cat!) but it covers windows/breaking glass. the only time we'e had problems is when we have forgotten to turn it off before we tried to leave the house (duh!) or when the winds were high, and rattled the shed doors too hard. it took a little adjustment time for us, and some tweaking by the installer, but it seems to be "right", now--and hubby, who has parkinson's, feels safer. so do i. the response time via phone has always been super quick (ask me how i know--and if i remembered to turn off the alarm!) and the police dispatch for checking on us has been super fast, too.
it is worth the peace of mind, at least for us.