This week NBC 5 has been doing a daily report called Five Nights that Could Save Your Life. Yesterday, the report was about smoke alarms.
NBC link to the report here.
There are two types of smoke alarms. Ionization and photoelectric. Most of us have the ionization ones. When doing their test, with the help of a fire marshal, the NBC reporting team noticed the ionization alarms went off nearly 30 minutes after the photoelectric ones (four were used in the first demonstration). The difference between the two seems to be that the photoelectric alarms recognize smoke, whereas the ionization alarms are more likely to be activated when flames occur.
Look for an I or a P on the back of your smoke alarm and if it doesn't show that you have a photoelectric (P) alarm either buy one and use both or buy one that is a dual sensor alarm (both I and P).