A much discussed subject but today I hit on one possible solution .Was putting in some smoke alarms and on doing the final connection at the consumer unit I noticed the bell transformer was connected to the ring main ( no fcu 1mm cable ) and the thought hit me why not put the bell transformer on the alarm MCB? Then if the door bell stops working you would know the alarms were off as well, hence to test there is mains to the alarms just press the door bell. This idea could be taken even further if you were to put the transformer at the end of the line of alarms , this would test there was power to all of the alarms.
Just a thought, what do other people think?
Steve
BTW if you thought blue/brown twin and earth looks odd what till you get your first reel of black/grey/brown 3core and earth , it's going to take some getting used to.