Your phone is supposed to be a phone, not a hand-warmer. So why does it, at times, feel like it could barbeque your palm? The components in your phone or tablet – the screen (which it’s easy to forget is actually powered by a tiny light bulb), the GPS, the camera, the processor – draw electricity from the battery. When they do so, they aren’t completely efficient: They always waste some energy, which is released in the form of heat. By measuring how hot your phone gets, you could figure out how inefficient its electronics are.