right.... found out what it is....

I have been driving the car for the last 18 months with a plain key (no chip in the key due to being bypassed before i owned the car when an alarm was fitted). Today it decides it wants to read a chipped key again!! why is this? and also how would they have bypassed the chip?
I only found this out because i tried my spare key (still a plain one) and this one (the old door key) was next to it... so now i have to put the ignition key in and wave the old door key around the barrel ..