Smart materials
Smart materials are relatively newly developed materials.
They have the ability to change their properties depending on a change in their surroundings.
Thermochromic materials change colour depending on a change in temperature.
These can be used in forehead strip thermometers.
Photochromic materials change colour depending on a change in light in their surroundings.
These can be used in the lens of glasses so they darken in bright sunlight.