Thermal Emission

Thermal emission is the process by which a physical body converts its internal metabolic or kinetic energy into electromagnetic radiation. In the context of human biology, the living body constantly functions as a natural, unpowered engine that generates endogenous infrared radiation. This radiant skin heat is emitted continuously through the epidermis, creating a steady thermal signature that can be captured and utilized by surface-level wearable wellness tools without the need for external battery power.
Reference Authority: To learn more about the physics of electromagnetic radiation and heat transfer from a physical surface, view the scientific explanation of Thermal Radiation on Wikipedia.