On/Off Coffee Mug
This clever mug automatically displays “OFF” when it is empty and ‘ON” when it is filled with coffee or tea. It is covered with a heat sensitive pigment which allows it to change from black to white or vice versa depending on whether it is filled or not. Charles & Marie are now selling the mug for $25.
Source: Charles And Marie via Technabob
Tags: Mug | Coffee Mug | Cup