Here is a wearable device that warms your body up using dual temperature sensors and a smart algorithm. Sola can increase your core body temperature by 0.4°F. The device is lightweight and looks like a regular smartphone running armband. It has LEDs and space for your keys.
Sola has a 2000 mAh battery that lasts up to 2 hours. It can be charged via USB. You can get it on Indiegogo.