But you would be adding an entry zone, then probably making another detector access. Which would mean if you back door was smashed in ( sorry had to say that) the entry timers would start, the theif would have 30 seconds to run about warned the alarm was about to go off and run away before the bells went and he would have a armfull of goods.
The above is why systems are best left to professionals to design.
Alarm, August 2011
