Yeah a fault code scanner should pick up any issues in the alarm/CL/ccm (Comfort Control Module), if any present.
Have you disconnected the battery recently?
I find with this car, pulling the battery and reconnecting it within the space of 5-10 mins causes quirks with the Central locking interface. Such as the windows not remembering one touch, one touch only working on one side, only 1 door unlocking (driver's side usually), keyfobs not working etc.
When that happens I pull the battery for at least an hour and it all comes good again. It may not solve your problem but it's worth a try.