So we have six or seven smoke detectors at home. They are wired into the building's main power, but they also have a battery backup. Apparently, the detector sends a check regularly through the battery to check its voltage and ensure that it is in working order. If that voltage (maybe current? Dammit Jim, I'm a geologist not an electrician!) is too low to run the detector, then the detector chirps.
Perhaps this is common knowledge to people, but last night I had a bit of a situation as all four upstairs and one downstairs detector began chirping when we were heading to bed. They did this for half an hour. I tried pushing the silence button (which usually works), and changed out the batteries in them. Nothing worked.
Now to forestall any admonishments, I know you're supposed to change out the batteries every 6 months. I just wish they lasted that long. These things have been 9-volt vampires and end up getting changed when they chirp.
Finally out of frustration, I called our property manager and asked him if he had any tricks to get them to be quiet. (And yes, they did chirp a few times during the conversation.) He said to completely disconnect the ones that were chirping completely from power. I ended up only having to do that to two of them before they all quieted down.
Apparently there are new code laws coming into effect in 2015, and so next year we will be getting new detectors that have their own 10-year battery life and not be connected to power. He is coming by today to install three of the new detectors in the most important locations: master bedroom, guest bedroom, and upstairs hallway. The rest will get replaced next year.