Why is my Kidde smoke detector blinking red every 15 seconds?

According to the Kidde Smoke and Carbon Monoxide Alarm user guide, a red LED light blinking every 15 seconds indicates a low battery condition. This means that the batteries in your smoke detector need to be replaced. When the batteries are low, the red LED light will flash and the unit will "chirp" once every 60 seconds for at least 7 days. To resolve this issue, you should replace the batteries with new ones. The user guide provides instructions on how to properly replace the batteries in your specific model of smoke detector. Once the batteries are replaced, the blinking red light should stop, and the smoke detector will return to normal operation.