Fire safety and prevention of combustible materials are of paramount importance in modern society but have been a global challenge. Frequent fire disasters cause massive casualties and irreparable property losses and negatively impact the global environment. A recent increasing concern is to develop smart fire warning materials and sensors that combine traditional passive flame retardant strategies and active fire alarm response. However, there still lacks an incisive and comparative overview of such fire warning systems. This review comprehensively discusses passive flame retardant materials, traditional active fire warning sensors, and next-generation smart fire warning materials and sensors, in addition to the flammability of combustible materials. The conceptual design, synthesis, characterizations, and fabrication strategies of smart warning materials are systematically reviewed. Subsequently, the performance and applications of different fire warning sensor systems, including resistance-type, phase/shape change, thermoelectric responsive and colour-change observation, were reviewed and compared to understand their features and working mechanisms better. Finally, some key challenges associated with fire warning materials/sensors are highlighted, following which future perspectives and opportunities are proposed.