Home Inspectors will make note of the absence of smoke detectors but will hesitate to speculate on their working order and service life. Most inspectors will do the same for carbon monoxide (CO) detectors.
CMHC recommends every home have at least one CO detector. If you live in an older house with an older furnace, I suspect CMHC would strongly recommend the installation of a detector.
The quality and service life of CO detectors vary considerably but minimum performance standards must be met by manufactures. On top of reading the warranty it is suggested the CO detector be replaced every 5 years.
Installing a CO detector does not mean you don't have to inspect and maintain your gas and wood burning appliances. Installation should be viewed as a back-up precaution.
Calgary is a cold city and our furnaces go hard during the winter. That time of the year is approaching and it might be a good idea to give some thought to checking, replacing or buying a new detector.