Users simply stick the Solar Chaser in a sunny window, using its built-in suction cups. Once its power switch is flipped and sunlight hits its panel, it will begin swinging and jigging its arm, causing a toy attached to a ribbon at its end to dance around. As long as the sun keeps shining (even indirectly, apparently), the cat can keep playing.
The arm can also be detached, for use by hand.
The Solar Chaser is priced at US$39.95, and can be seen in use in the video below.