Are smoke detectors and carbon monoxide detectors important?

Are seat belts important?  When was the last time you used them?   I talk about how important it is to replace smoke detectors every 10 years, but what about carbon monoxide (CO) detectors?  They have a similar issue.  They lose sensitivity over time.  Manufacturers recommend replacing them every 5 years.  (Some now have ones that last 7 years.)  Our web site's Helpful Hints section has more detail, but why would you not replace them?  And when you do, write the date on them for when they should be replaced, eg: "Replace March 2016".  Safety sometimes means doing small things to avoid big risks.