Veritas 8 burglar alarm - alarm goes off randomly ?

Had the Veritas 8 burglar alarm fitted few years ago, but over recent months the alarm will go off in middle of night for no apparent reason?
Each time the alarm panel indicates different pir sensors but there appears nothing wrong with them?
I have read that it could be due to battery problem i.e., battery is knackered and when drop in mains power, the battery does not kick in,...or also that htere is a fuse inside alarm panel to battery that is blown.
pLEASE HELP AS i AM WRITING THIS AT 4AM AFTER ALARM HAS GONE OFF AGAIN WAKING ALL!
THANK YOU IN ANTICIPATION