Using modeling and computer simulation techniques, we conducted a comprehensive analysis of heat propagation processes and noise determination in a nanoscale three-layer detection pixel of a thermoelectric single-photon detector. The detection pixel comprises an absorber, a thermoelectric sensor, and a heat sink stacked on top of each other on a dielectric substrate. Our research was aimed at studying the spread of heat inside the detection pixel following the absorption of single photons with energies ranging from 0.8 to 7.1 eV (1550–175 nm) in tungsten or molybdenum absorbers of various thicknesses. The simulation was executed based on the equation for heat propagation within a limited volume. We explored temporal temperature variations in different regions of the detection pixel and analyzed the average temperature gradient across the sensor and heat sink surfaces. Parameters such as signal power resulting from the photon absorption, equivalent noise power, and signal-to-noise ratio were determined. Our results indicate that detection pixels consisting of W or Mo absorbers, a thermoelectric sensor La0.99Ce0.01B6, and a Mo heat sink, with a 15 nm thick absorber and a surface area of 1 μm2, can effectively detect single photons across a broad spectrum from far ultraviolet to near infrared. The calculated signal-to-noise ratios and temporal characteristics indicate the possibility of using this thermoelectric detection pixel design in optical microchips and large-scale multi-pixel cameras.