Cup for the blind / cup

This cup has a vacuum structure like a thermos bottle, which makes an echo sound while water is filled in. As the water level rises, there is less air in the cup and the echo sound gets a higher pitch, which is easy to hear. This helps blind people to "hear" the water level and to know when to turn off the tap. When filling very hot water into a cup from a kettle, for example, blind people might get scalded if they can’t tell when the water has reached the top. This cup solves that problem.