Your smoke alarm should be installed in the middle of the room or at least 50cm from any obstacle (as far as possible from the wall), with a minimum of one smoke alarm per floor (ideally one per room). The best areas to install your smoke alarm will be in hallways and stairways, close or in each room.

It is highly recommended to not place your smoke alarm in kitchen or bathroom: smoke and vapors could cause false alarms. Please also avoid garages, laundries, fire places where combustible particles could disturb your alarm, and all locations close to airstreams.
In these areas its preferable to install thermal alarms instead.