ive fire angel interlinked alarms - I got them as Mrs Moonshine is deaf and can't hear the fire alarms / burglar alarms and they used to do pairing to vibrating bed pad and strobe and a low frequency sounder.
I had problems with the vibrating Pad and strobe losing its pairing from the rest and it issues an irritating warning chirp - Mrs Moonshine can't hear that - but I can
and it kept waking me - so I binned the Bed pad and strobe and we rely off the Low frequency sounder - its loud!!!
other than that I've hadno problems with them (the LF sounder very occasionally indicates a dropped link in the network by means of a flashing error light, but this seems to resolve itself quickly) and I fitted all the additional ones as per Scottish regs last year before the reg implementation was postponed - but not worried about it - its a good idea.
My Burglar Alarm bod fits interlinked alarms too - he doesn't use fire angel tho as they can be a but temperamental pairing and he wants reliability and not have to do repeat house calls to fix dropped pairings.