Sorry but this is proof of the failure of CO alarms listed to UL 2034 or 2075. One died and several ill while the alarms finally alerted. UL listed CO alarms are designed to alert only once your COHb has reached 10% meaning you already have CO poisoning if it alerts. Gee thanks. They are also unreliable.
Get unlisted CO monitors to protect your family. Replace smoke alarms over 10 yrs old with dual sensor photo and ionization type alarms and replace batteries annually. You can remember to change them every yr the week of Oct. 9th, which is Nat'l Fire Prevention Week. Don't forget to vacuum the sensor slots with an upholstery brush attachment . Also, note that hitting the test button only ensures the electrical circuilt is intact--it does not test the sensor's function or sensitivity.