One of the smoke alarms began to beep periodically, freaking us out. Since there wasn't any smoke in the house, we figured that it was either telling us it needed a new battery, or that something else was otherwise wrong with it. After putting in a new battery, it stopped beeping but was still blinking red once in a while.
The stack of manuals that was in the house when we bought it did not include one for the smoke alarms. So it was Google to the rescue once again. A quick search for "Firex 120-1182" turned up a vendor that included the PDF manual and specifications on their
website. Now that's a good sales pitch, in my opinion!
Anyway, the red-blink once every 40 seconds was normal, just checking the battery level. All the other alarms were also doing it, we just didn't pay any attention to them because they're just those "work quietly in the background" things.
So what would _you_ do when something in the house starts acting weird? Start practising your Google-Fu now.