Looking to add warmth to your outdoor activity? The Fieldsheer powered by Mobile Warming Technology Bluetooth®-enabled Primer heated baselayer shirt offers light-weight performance and an integrated Far-Infrared heating system. The Primer is a next-generation baselayer that delivers 7.4-volts of instant heat for hours through our exclusive Bluetooth®-enabled built-in touch control button. Use the free MW Connect™ app to adjust temperature or check battery levels. Choose from 4 heat settings to keep you warm and comfortable for hours.