<P> The rear - view mirror is augmented by one or more side - view mirrors, which serve as the only rear - vision mirrors on motorcycles and bicycles . </P> <P> Among the rear - view mirror's early uses is a mention by Dorothy Levitt in her 1909 book The Woman and the Car which noted that women should "carry a little hand - mirror in a convenient place when driving" so they may "hold the mirror aloft from time to time in order to see behind while driving in traffic". However, earlier use is described in 1906, in a trade magazine noting mirrors for showing what is coming behind now popular on closed bodied automobiles, and to likely be widely adopted in a short time . The same year, a Mr. Henri Cain from France patented a "Warning mirror for automobiles". The Argus Dash Mirror, adjustable to any position to see the road behind, appeared in 1908 . Earliest known rear - view mirror mounted on a racing vehicle appeared on Ray Harroun's Marmon race car at the inaugural Indianapolis 500 race in 1911 . Harroun himself claimed he got the idea from seeing a mirror used for a similar purpose on a horse - drawn vehicle in 1904 . Harroun also claimed that the mirror vibrated constantly due to the rough brick surface, and it was rendered largely useless . </P> <P> Elmer Berger is usually credited with inventing the rear - view mirror, though in fact he was the first to patent it (1921) and develop it for incorporation into production streetgoing automobiles by his Berger and Company . </P> <P> Recently, rear - view video cameras have been built into many new model cars, this was partially in response to the rear - view mirrors' inability to show the road directly behind the car, due to the rear deck or trunk obscuring as much as 3--5 metres (10--15 feet) of road behind the car . As many as 50 small children are killed by SUVs every year in the USA because the driver cannot see them in their rear - view mirrors . Camera systems are usually mounted to the rear bumper or lower parts of the car, allowing for better rear visibility . </P>

What is the button on the rear view mirror