Betsy I have no experience with the wired in ones, but the battery only ones I've used all get low battery after 6 months or so. It's always at 3:30 in the morning too, makes one wonder about the sadism of the designers.
I would be suspicious about the situation your friend has, it does not sound correct that alarms with good batteries beep and the bad one doesn't I'd call the manufacturere and see if they know. Of course they were probably made in china and have high levels of fake protine! <GRIN> tom Fowle
