<p>Continuous accurate monitoring of body temperature is a core function of smart wearable temperature sensors. However, due to delay of heat transfer, their temperature response parameters are difficult to characterize in real time. It is challenging to prepare a temperature sensor with high sensitivity, fast response, as well as enhanced sensitivity in the physiologically relevant temperature range (30–50°C). Here, using natural polysaccharide sodium alginate (SA), acrylamide (AM), and <i>in situ</i> polymerized polypyrrole (PPy), a conductive hydrogel (SA/PAM/PPy) was synthesized. The temperature response feature of SA/PAM/PPy was characterized via an instant photothermal conversion (IPTC) system, capturing the response times of the temperature rise and the temperature drop. The conductivity of the hydrogel increases with pyrrole concentration, rising from 21.3 mS cm⁻¹ at 10% Py to 67.7 mS cm⁻¹ at 70% Py. By reducing the hydrogel thickness to 1&#xa0;mm, its temperature response feature was improved with the temperature rise/drop to 0.1185&#xa0;s/0.1957&#xa0;s, respectively. The temperature sensitivity of hydrogels varies with temperature ranges. At 10–30°C the temperature coefficient of resistance (<i>TCR</i>) is −1.22% °C⁻¹, and at 30–50°C it increases to −3.70% °C⁻¹, demonstrating enhanced sensitivity in the physiologically relevant range. After 500 cycles of mechanical fatigue and temperature sensing, the hydrogel still exhibits a stable relative resistance change, indicating reliable sensing performance. It can be applied to effectively monitor changes in human body temperature during running exercises at different speeds (4&#xa0;km h⁻¹, 8&#xa0;km&#xa0;h⁻¹, and 10&#xa0;km&#xa0;h⁻¹). Overall, the developed hydrogels not only sense temperature variations but also exhibit optimized performance in the physiologically relevant temperature range, showing great potential in smart wearable technology.</p> Graphical Abstract <p></p>