Use several different systems. For example this is $26. It simply triggers on motion and calls several phone numbers of your choosing.
http://www.amazon.com/Security-Burglar-Alarm-System-Dialer/dp/B000SMM1DY/ref=sr_1_1?s=hi&ie=UTF8&qid=1324613281&sr=1-1
One needs a land-line for this $26 unit.
That excludes me.