In a former life I worked for a company that supplied the motion detectors, glassbreak sensors, and magnetic switches to ADT. For that matter, we supplied the smoke detectors and CO detectors as well.
I know when I was working there we were working on "pet immune" motion detectors. ADT was losing money every time one of their detectors went off. They did the math and came back and told us it was actually cheaper for them to pay off on a robbery where the alarm didn't go off then to have false alarms.
It's been 11 years since I worked there. I know you need to have power to the area, and when I was there they required a phone line. Nowadays they probably will also do a cell phone type installation if you have service in the area.
The problem is that the motion detectors only work once the thief is inside. Of course, once the thief is inside, they can take what they want and be gone in 5-10 minutes, which might be well before law enforcement shows up, especially if it is a remote area.
So, if you do a motion detector install, you'll want a two stage entry point. The first would be a simple wood structure at the entrance. This would house a motion detector, which wouldn't go off until the thief got inside the structure. Then you do your "hard to open" lock, etc where they would have to spend some time to get it open. This would give the local law enforcement a chance to respond and nail the bad guys.
It also wouldn't hurt to have a game camera set up to snap a photo, just in case they didn't make it through the second door, or in the even the law enforcement didn't show up.