When positioning a smoke alarm, it is important that you avoid anything that will prevent smoke from reaching the alarm. For instance, if there is an air vent in the ceiling it may divert smoke away from the alarm.
Also, it is important that you avoid anything that causes nuisance triggering of the alarm, because this can lead to the occupant of the dwelling removing the alarm altogether.
Electrical noise sources such as ceiling fans, fluorescent lights and LED lights can create electrical noise that triggers smoke alarms.
When installing smoke alarms, it is a good idea to locate them 1 metre away from ceiling fans or lights. Check the user guide for the model being installed as some models recommend less than this.