I had my alarm system installed in December of '07. In October of 2010 two of the sensors on two of the doors started to malfunction at the same time. The alarm didn't sound when these two doors opened. Now I am told that each of the sensors for the doors will cost $21.00 plus a service visit of $89.00. Just when it's time to renew the contract at a cost of $119.00 for the year. I was told that the life expectantsy is about 4-5 years on these sensors. These are only 3 years.