First Alert - CO615 Carbon Monoxide Plug-In Alarm with Battery Backup CO615 - White

Thank you for your question. Relying on the backup battery as the main power source will necessitate frequent battery changes. Battery backup on this First Alert carbon monoxide alarm keeps it working even during a power outage for added peace of mind and security. If you have any additional questions, please don’t hesitate to reach out to our First Alert Consumer Support team at 1 (800)-323-9005.

Thank you for your question, Sandee. The date of manufacture will be located on the back of the unit. If you have any additional questions, please don't hesitate to contact our Support Team at 1(800)-323-9005.

Since CO is slightly less dense than air the higher the detector is placed is better. "If you use plug-in CO detectors, find the highest outlet to place them. A detector near the floor may not sound an alarm quickly enough to keep you safe. If you use detectors that provide periodic readouts of CO levels, place them high enough to read to monitor CO levels."

Yes

No, during normal operation, this unit does not chirp every 90 seconds. The following should help explain the chirps/beeps: What Do the Beeps From Your Carbon Monoxide Alarm Indicate? * 4 Beeps and a Pause: EMERGENCY. This means that carbon monoxide has been detected in the area, you should move to fresh air and call 9-1-1. * 1 Beep Every Minute: Low Battery. It is time to replace the batteries in your carbon monoxide alarm. * 5 Beeps Every Minute: End of Life. This type of chirp indicates it is time to replace your carbon monoxide alarm. The above information was taken from https://www.firstalert.com/community/safety-corner/what-does-the-beep-mean