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[Display omitted] • A flexible thermoelectric nanocoating with layered heterostructure was constructed. • The nanocoating exhibited accurate detection capability for the temperature rise stage of a fire. • The nanocoating triggered fire-warning within 1.5 s when encountering fire. • The coated polymer materials were difficult to be ignited during burning tests. Thermoelectric materials have attracted considerable interest in the field of fire warning because of the accuracy and repeatability of their thermoelectric effect. Nevertheless, the incompatibility between high thermoelectric efficiency and flexibility restricts their application in flexible electronic materials. Herein, the dilemma was overcome by constructing a flexible thermoelectric nanocoating with layered heterostructure through the co-assembly of thermoelectric graphene (TEG) nanosheets and carboxymethyl cellulose (CCS). Layered heterostructure not only exhibited exceptional flexibility, but also enabled repeatable sensitive thermosensation of the nanocoating. The nanocoating could accurately monitor the temperature rise stage (50–350 ℃) of a fire, and trigger the fire-warning within 1.5 s when encountering flame. Even it was reburned, the nanocoating still triggered the fire-warning within 2.6 s. Besides, the compact layered structure endowed the nanocoating with efficient flame retardancy. The coated polyester film reached a limiting oxygen index of 33.7 % and self-extinguished in vertical burning test. This flexible thermoelectric nanocoating may pave the way toward high fire safety for flexible electronic materials. [ABSTRACT FROM AUTHOR]