SlackAlice, if you're really hard of hearing there are even vibrating pads which fit under your pillow and operate when the smoke alarm goes off. We fit these occasionally if the person meets certain criteria (ie if they live alone and are completely deaf.
Builder, I usually fit them 1 - 1.5m from the kitchen door because in many cases that's where the stairs (and the opening for the landing) are. If the person does follow my advice and keeps the door closed when cooking then the door should hold back a fire and the majority of the smoke. A small amount of smoke will escape from around the frame which should be enough to set the alarm off as it rises up the stairs. If the alarm is closer to the front door (I see loads like this) then in my opinion it has less chance of activating in the above example.
I do always advise people not to leave the kitchen when cooking but I know this sometimes happens (to answer the door, check on the kids, watch telly etc) so in my mind I'm trying to ensure that the alarm will operate when the door is closed and only a small amount of smoke is present.