Same happened to us. bF (Battery Fault) displayed. Alarm went off when we were on hols. Instead of checking our property externally our miserable neighbours reported it to Environmental Services and we got call. Fortunately we have key holder and matter easily resolved. Called engineer today, simple 5 min job to remove control lid (internal sounder activates) removes pos and neg connections from battery, replaced battery, re-connects leads, closes control panel lid - all the time internal sounder is going off but then MAGIC - enter our personal code couple of times and panel reverts to day-state. Checked thoroughly and everything works !! NO Engineer code needed just need to have replacement battery to hand when you remove the cover. Call out £50, Battery £25 well worth it. PS previous battery lasted 14 years, hope new one lasts as long.
Michael Gowonstoke, June 2014