I think I just came up with a use for old PCB etchant
There's something odd about the alarm designer's mind, IMHO. I have a couple of conventional mains operated, battery backed alarms in my house, and they beep to let you know when the battery needs changing.
OK? Sure, in theory.
They don't have a clock, so when it's time for a new battery, they beep. Even if it is 2am. Once per minute. Beep.... beep.... beep....
So, I stumble out of bed, reach up, remove the old battery and replace it with a new one. I even swap them both at the same time, because if one has decided to wake me up in the middle of the night, the other will only do the same a week later.
Fit the new battery, close the little drawer, and...
Beep...
beep....beep....
beep....beep....
beep....Oh, FFS, they're both at it now. And there's no way to shut them up. You just have to wait, about 15 minutes, and then they'll definitely shut up on their own. At least, I think that's how it works; no idea why, and it's a few years since I last had to do this. Anyone seen the manual? (Sheesh, how hard can this be, it's only got one button and I don't think that actually does anything at all anyway). Oh, great, now the cat's awake and wants his breakfast.
beep....
beep....beep....
...silence? Did the downstairs one beep too?.... ...beep......beep......beep...Finally I can get back to sleep. Morning comes. Coffee. Breakfast. Then:
!!TOAST!! SOMEONE'S MAKING TOAST!! WARNING!! EVACUATE!! TOAST!!! OMG WE'RE ALL GOING TO DIE IN A TOAST FIRE!!!