Help with Ademco Vista 20P Security System odd problem

I have a home Ademco Vista 20P security system. It is 4 1/2 years olds and has worked fine until now. On the disaplay panel it has a zone number, 10, and "bat" flashing. The zone number refers to an entry door that is hard wired. I thought the system back up battery was probably going bad and replaced it. This did not solve the problem. What is strange is this entry door alarms when I have system in "away" or "chime" mode but not when it is in "stay" mode. As I said it is hard wired so I find it stargne "bat" is showing up in the display panel. Any idea what is causing this and what needs to be done to correct the problme?

 

Jeff
Thanks for the comments. On my the codes I was given for each of my zones, zone 10 is an entry door from the garage. I thought it, along with the other entry doors were hard wired. I know the sensor has wires comeing out of it. They run back into the door frame and not sure where a battery would be located. Is there any way to check out to to see if it is wired or wireless? Also where would I look for the loaction of the battery?I rechecked the central control panel. The only battery in there is the 12 volt back up battery which I replaced.

 

Jeff
I did find a wireless device. It is a Honeywell 5800MIRCA. It appears to be a sealed device that will need to be replace versus relacing a battery. I am guessing there is a battery inside the unit. I did check in on the interenet to see what it was and the description says the battery lasts 10 years. It made 4 1/2. Another interesting part of this is it not in the door jam on the side. It is on the bottom on the door threshold with the maganet holder inbeded into the bottom of the door. Again thanks so much for taking the time to help. I doubt I would have found it otherwise.
John

 

Jeff
Yes, I am up North in Cincinnati. Already tried of winter. I don't want to sound like a pest, but I do have one last question. The piece or component with the magnet is recessed into the bottom of the door. The other component is the sensor with a long wire coming out of it, which is in the threshold. It has a while top and orange bottom. I am taking it the battery is inside the white and orange sensor. Can this be opened and just replace the battery or do I need to replace the whole device?
Again thanks for all your help.
John

 

Jeff
Never mind. I did figure out how to get the top off and see it is a coin battery. I can not again thank you enough for your insite and help. Have a Merry Christmas.
John