a Photograph of the large-area compliant TEG and an flexible printed circuit board (f-PCB) with a step-up voltage converter and five light-emitting diodes (LEDs). The right photograph is enlarge view of the f-PCB. Scale bar, 2 cm and 3 mm. b Circuit diagram and optical image of the f-PCB for step-up voltage conversion and LED operation. The block diagram shows an operating sequence with the output voltage and power after each block. c Input and output voltages of the step-up converter when the TEG was put on a hot plate. d Real-time optical and infrared images of the compliant TEG with a step-up voltage converter after the TEG was put on a hot plate. The photographs show that the LEDs was turned on immediately after the TEG was in contact with the hot plate. The infrared images show the temperature of the upper surface of the TEG. Scale bars, 2 cm. e Schematic illustration of hot surface warning gloves with a self-powered LED system and light masking packages. f Photographs showing a demonstration of the TEG-attached gloves when they are used to grasp various hot objects such as a bottle and a kettle. The insets show enlarged view of the self-powered system and packages. The conformal contact between the TEG-attached gloves and the 3D surfaces of the heat sources results in a bright “H” sign without any assistance from an external power supply. Scale bars, 5, 5 cm, and 5 mm.