You should have one smoke alarm on each floor of the house, in a central hallway location. They should be placed on the ceiling, at least 30cm from a light fitting. This diagram shows ideal placement location in a 2-storey home:
This image shows ideal minimum smoke alarm placements.
For more information relating to positioning smoke alarms and building regulations.
For further information about different types of alarms and guidance on fitting click here.
All smoke alarms should be tested once a week. To do this press the test button on the alarm (usually a circular button in the middle). The alarm should sound, then stop.