The interior motion sensors are programmed to turn off if the top is down. The red clip "fools" the sensors into thinking that the top is up.

(Hint - some have made their clip black so it is not as noticeable by using spray paint or permanent marker)

Charcoal filters also act to absorb toxic and foul-smelling gases such as ozone, nitrogen oxide, sulphur dioxide and hydro-carbons.

Recommended replacement is every 12,0000 to 15,000 miles or once a year.