Most police departments even with a quick response time don't show up fast enough.Where we live, the police arrive very quickly. We found out the hard way, and help was there before we knew what was up.
I agree that the loud noise and knowing they are in your house is good. You don't need to pay for monitoring for that. But I understand people doing that.I don't ever assume that the police will respond to my alarm going off but my intent for getting a home alarm system was to (1) alert me that someone is trying to get into my house when I am home and (2) will hopefully scare off a would-be intruder when said alarm goes off if they were to break into my house quickly whether I am home or not.
An alarm going off may not deter all burglars but they will know that a loud noise is likely to draw attention so their time in my home will hopefully be short since the clock is ticking versus someone who just has a dog barking at them if I weren't home. My neighbors would never bat an eye at a barking dog.
I am not a fan of just glass break as it doesn't deter someone from jimmying a window open when I am home. Same goes for just having motion detectors as a primary. Motion detectors need to be turned off if occupants are home. I paid extra to have a sensor on EVERY door and window. I worry about my personal safety while I am home. Stuff can be replaced, people not so much.
I pay about $45 a month for ATT Digital Life.
I've known several people with alarm systems who have been burglarized and the police never caught the in burglars.
My biggest point was that I would worry more about making my house difficult to break into and protecting my belongings (StrikeMasters, NightLocks, a large safe that can't be moved).