Just because the Rig is 2 years does not mean the detector can not be older
Is the Detctor "Self Powered" after 2 years it needs new batteries
or is it 12 volt house powered.. Above comments about low batteries.
Now. Each detector has multiple alarm patterns. For example on common brand
BEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE CO Smoke or Explosive Gas depending on the detector
Beep (long pause) Beep (long pause) BEEP continuing forever
Low battery or internal issue detected or TOO OLD.
NOTE that is ONE BRAND. other brands may code differently.