An interesting mug that reacts to heat…
Coffee mug reacting to the heat (hot beverage)
In its dormant state, the mug offers a black “OFF” display, but once your hot coffee or tea hits the inside, it gradually transforms to read “ON”. A heat sensitive pigment changes the color of the mug from black to white. [Technabob]
The colour-changing is nice, but the “On-off” word doesn’t really appeal to me. Perhaps they should try some other words or patterns instead.