I did a bit research on line and found there are security system being sold on the internet (search alarm system on ebay). They are about 200 dollars with everything you need. The best part of this system is the control panel has auto dialing feature. When something happened, either fire or somebody breaking in your house, the system will automatically dial out to your preset numbers.
Think about this. You pay 20 dollars to the security companies. You simply let the system to call the company instead of yourself. The company when received the call will need to call you to confirm the actions to take. So you need to take the call anyway. Why bother having the company in between and ripping you off?
I'm sure this is a big rip off that not many people have realised yet.