Whether you are on the mountain, at an outdoor concert, sporting event, or shoveling your driveway- when the weather turns blustery, turn to Heat Pro Hand Warmers. Average activated temperature is 57°C/135°F. Whether you are on the mountain, at an outdoor concert, sporting event, or shoveling your driveway- when the weather turns blustery, turn to Heat Pro Hand Warmers. Heat Pro Hand Warmers are activated as soon as you open the package and reach maximum heat within 20 minutes. With Heat Pro Hand Warmers, you won't even know it's winter.