The answer to 'what size smoke detector do I need' is that the size of smoke detector you need depends on the size of the room or area it needs to cover. Typically, a standard 6-inch diameter smoke detector is suitable for most residential rooms and hallways up to 900 square feet. For larger spaces, you may need a larger 9-inch or 12-inch diameter smoke detector to ensure proper coverage and detection.
It's important to follow the manufacturer's recommendations for the appropriate size based on the room dimensions. Placing the right size smoke detector in each room is crucial for ensuring your home is properly protected in the event of a fire.