Help with TD5 in Malawi

I disarmed my immobilizer with the EKA code so that I can just open the car with my key in the door lock. I did this because buying a new key fob is crazy expensive here in Malawi. However, when I tried to start it, the battery was flat and the alarm started to go off. I was surprised because I thought I had disarmed the alarm. Can anyone explain what is happening?:boxing:
Thanks,
Mark

If the alarm is going off surely the battery ain't flat? Does it have an immobiliser?

Yes it does but I thought I had disarmed it with the code. I had been opening the doors with the key without any sign of the alarm being on.