The smoke detector is the 20th in the 3rd catalog (Snooty Foodie), making it the 40th item altogether. It resembles a standard smoke detector, with a white cover and 4 streaks showing air vents. A red light is present as well.
When burned, the item will beep with long beeps and short pauses. The fireplace will start to rain, dousing any flames.
It is currently in [???] combos: