Answer: A smoke detector.
Researchers from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, have developed a wallpaper that is not only heat resistant, but also capable of sounding the alarm when it detects a fire. They found that hydroxyapatite, a material in bones and teeth, could be made into long nanowires and used as the base for wallpaper. The material is both heat resistant and environmentally friendly.
The wallpaper can sound the alarm in the event of a fire thanks to an electrical circuit embedded within it that is hooked up to an alarm. The circuit is insulated by a graphene oxide ink mixture that prevents the flow of electricity at room temperature, thus deactivating the alarm. Add heat, however, and the ink suddenly becomes conductive, completing the circuit and sounding the alarm within two seconds.