...I get alarm companies coming around all the time asking to set up a "free" system in my home and get you with the monitoring contract.
This is a major pet peeve of mine. Many of the major companies hook you with their $99 dollar offers and then rob you blind over the next 3 years or more with their monitoring contracts. Furthermore their systems can't (at least not easily) be reprogrammed to be independently monitored. The $30-40 difference they charge a month adds up. $35 X 36 months is over $1200 that could be put toward a dependable professionally installed system.
If you are having a system professionally installed, ask if it can be monitored independently. Don't get locked into an overpriced monitoring contract.
For those installing their own systems and choosing to monitor them themselves, I strongly recommend you find some friends or family that live by a phone 24/7. I don't care how many bars your cell phone company says they have, you can not rely on your cell phone having a signal 24/7. If you home is broken into or catches fire, you need to know ASAP.