The security system we have at home is with Vivint. It is a wireless 24/7 monitoring service that has been reliable. I like it a lot. However it was installed by one of their service reps with no upfront cost...but there is a $49 / month monitoring fee.
However at the farm any security system that relies on cell phone coverage would not work as we do not have sufficient strength cell coverage over our property.
I had to install a buried WiFi cable for 1/4 mile down the length of our valley to connect our shop building and new house site. That cable installation alone cost $3600...three years ago.
However having WiFi then allows the installation of multiple WiFi cameras anywhere within about 100 ft of any building along that cable. Those cameras also have night vision and can then be monitored real time from any PC. The cameras are battery powered for those times when power is lost... but must still have a 120 V source to keep the batteries charged. The cameras communicate via the WiFi to wherever and whatever device you chose to monitor the system. The wireless cameras are made by Foscam and cost from $80-$200 each. They allow you to move the camera field of view and to zoom in and out remotely using the supplied software.
http://foscam.us/wireless-ip-cameras.html/
Some of the cameras have movement detectors which can automatically trigger a recorder to save a digital image of an incursion. Only problem is that cows, deer and coyotes can also trip the system. However if you are monitoring the system remotely and see a suspicious person or vehicle...you can manually record the event as well.
Rick...if your garage is less than 100 ft from you house a wireless system would work. I would think a self installed system like the Simplisafe would be sufficient....but I have no personal experience with them. Even then you would still have a monthly monitoring fee.
You likely would not need cameras but just simple interior movement detectors and a garage door sensor with entry door sensor. Your windows could have sensors added but it's not absolutely necessary with interior movement detectors.