I recently got this video sent to me via e-mail and it really opened my eyes to the effectiveness of my smoke alarm.  Recent studies have shown that children (ages 3-12, in this study) do not hear smoke alarms when they go off.  They sleep right through them!  This is due to their sleep patterns and brain functioning - they simply do not hear the alarm.  (Ever walked in on your child sleeping through an alarm clock?)  The good news is that there are now alarms in production that allow parents to record a voice message along with the alarm.  The study showed that children do wake up to the sound of their parents' voices.  To learn more watch this video.  (It may take some time to load.)  I will post information on the voice alarms as soon as I find it.