Commonly they look as such:



As you can see, there are many features which make this more than just some Thermos with a plug. It has timers, temperature controls (some even have a baby-formula temperature setting), and the all-important "lock" (Also known to unwitting foreigners as the "What the føk?" button after the most commonly uttered phrase while pounding the circuits out of the promising-looking large silver button in the middle and getting nothing but cold electronic indifference).
Still, it is pretty sweet when you want green tea and you want it now. Also good for instant coffee, instant ramen, instant corn soup, instant miso soup, and instant reasons to go to the hospital when you decide you can fill a teapot while watching the TV at the same time.
(BTW, You can't.)