Fire detector needs a new battery

Per Santa Clara County code, there is a fire alarm in every bedroom of the house, including hallways. Since we have a gas furnace, gas range, and a gas fireplace, I decided carbon monoxide detectors would be a good idea too. Each of my fire alarms is the same model -- a Kidde, talking combination fire alarm. It will tell you whether there is a fire or whether it's a carbon monoxide alert. There is a separate red light that blinks if the battery is low.

One night I was awoken by "{BEEP!} LOW BATTERY!" Thinking it was just a fluke, I ignored it and tried to go back to sleep. About 5 minutes later, I heard it again. "{BEEP!} LOW BATTERY!" Hmmm... guess I better investigate. I walked around the house and looked at each of the fire alarms. No lights were blinking, each had a green light on indicating it was plugged into the house's electrical system and working properly.

This went on for hours, with me and my wife almost going to bed, then hearing the beep and running to where we thought it was coming from, going from room to room trying not to wake the kids in the process. In the end I discovered that the red "low battery" light would illuminate only when the unit was beeping or talking.

The product manager for this product must have written an engineering or QA requirement that read something like this, "red LED light illuminates if battery is low," instead of "red LED light will help customer find fire detector with low battery." That would have made all the difference in the world.