Smoke Detector is the 20th item in the 3rd catalog (Snooty Foodie), making it the 40th item altogether. It resembles a standard smoke detector in real life, 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 in [???] combos: