We have had ADT for 17 years and I would recommend it without reservations. Since I have always had a cat (and always will) we did not install motion detectors. Ask them about a 'glass break'. Our two sheds (his and hers) are also armed and the siren is in one of the sheds. If you don't arm every entry - both windows and doors - there's no sense putting in a system. Also, if you have a doggie door make sure it's the kind with a rigid panel and lock that you can put over the flap when you arm the system. The bell is set to 'on' so it chimes everytime a door or window is opened.
Keep in mind that if you live in a rural area you have to consider the system a deterrent to scare and chase off intruders. We are rural and they'd be long gone by the time the sheriff arrived. The point is, they'd be gone before they could do any damage. This is the reason the siren is in the shed so it can be heard by everyone around.
Last year my husbands van was burglarized during a loud storm in the middle of the night. It was locked and parked only 6' from the house. We now have a gate across the driveway and lock it at night. The other gate is always locked. Nice areas are always more desirable targets than lesser well-kept neighborhoods.