The study of thermoelectric energy harvesting on people presented in this paper shows that although power generation is affected by many factors such as ambient temperature, wind speed, clothing thermal insulation, and a person's activity, it does not directly depend on metabolic rate as shown in the experiment. The relevant thermal properties of humans measured at different ambient conditions are reported. Several thermopiles are either attached with a strap directly to the skin or integrated into garments in different locations on human body, and power generation is extensively studied at different ambient conditions. Textile covering thermopiles is found not to essentially decrease power generation. Therefore, a hidden energy harvester is integrated into an office-style shirt and tested on people in real life. It generated power in 5-0.5 mW range at ambient temperatures of 15°C-27 °C, respectively. The thermoelectric shirt with such an energy harvester produces more energy during nine months of use (if worn 10 h/day) than the energy stored in alkaline batteries of the same thickness and weight.