A:Answer 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