This fire safety article ran in the San Francisco Chronicle last week regarding smoke detector safety. It’s the first time I had ever heard about the difference in how ionization and photoelectric smoke detectors operate.
According to the article, the ionization smoke detectors, which are more commonly used, trip more often when they are not supposed to, and don’t go off as soon as they should when they need to.
I just looked at the back of my smoke detector, and sure enough, it’s an ionization model. The issue seems to be the type of fire each responds to in an alarm.
Fire Safety Council review on best sensor type for kitchens (pdf format)