I had ADT for 2 years (the Norm is to make you sign up for 3 years, but I negotiated it to 2 years). After that I switch to Protect America, they are cheaper than ADT and provide 10 sensors (3 doors and 7 windows). All free and you install it yourself, not a rocket science. If you get confused about the installation, you can call them and they will walk you step by step. I got the wireless system, which runs around $45/month including all taxes. They even gave me $250 gift card for radioshack as a new customer (was an offer through Costco), but I really don’t know what to spend the radioshack money on.
I am happy with their system, they have the 10 sensors (vs 3 sensors with ADT), two remote controls (vs 1 remote with ADT) and two control panels (one keypad and one touch screen), also you can get the wireless plan and the cell phone app to control your system. They have many adds on such as glass brake sensor, light control, AC control, CO2 and fire alarm control, but in each service they are about 15-20% cheaper than ADT.