Checking out a left-behind Ademco

["runderwo@xxxxxxxxxxxx" <runderwo@xxxxxxxxxxxx>]

Moved into a house where the owner left behind an Ademco system.  I
don't see any identifying marks on or in the panel or on the box.  I
downloaded all the Ademco manuals but I'm not sure which one
applies... the Vista 20p looks "close" but it's hard to tell from the
pictures.  What would be tell-tale identification marks?  And how do I
get into the box without the proper key?  I would like to see what
shape the battery is in if nothing else.