I have a problem with my C&K Securitech 800L C031.165.01?

For some reason every time we open the front door or go into the garage (2 zones) when the alarm is off it beeps once, not sure why or how to stop this. It still allows us to set the alarm but can't seem to stop this 1 bleep when the alarm is off. Can't seem to find how to correct this in the manual. Any suggestions?