Photosensors

The mirror has a photosensor attached on both the front and back sides. During nighttime driving, these sensors detect distracting glare from vehicle headlights behind you and automatically dim the mirror to eliminate glare and preserve your vision. For this reason, use care not to cover the sensors with stickers, or other similar items. Periodically wipe the sensors clean using a piece of dry soft cotton cloth or an applicator.
Photosensors

The mirror has a photosensor attached on both the front and back sides. During nighttime driving, these sensors detect distracting glare from vehicle headlights behind you and automatically dim the mirror to eliminate glare and preserve your vision. For this reason, use care not to cover the sensors with stickers, or other similar items. Periodically wipe the sensors clean using a piece of dry soft cotton cloth or an applicator.

    See also:

    Checking the brake pedal reserve distance
    1) More than 2.56 in (65 mm) Depress the pedal with a force of approximately 66 lbf (294 N, 30 kgf) and measure the distance between the upper surface of the pedal pad and the floor. When th ...

    Forester in the Market
    The previous Forester was a Cars.com Best Bet on the strength of its versatility, reliability and safety credentials, but I've always had to footnote my recommendation of it with a warning about i ...

    Low tire pressure warning light (U.S.-spec. models)
    When the ignition switch is turned to the “ON” position, the low tire pressure warning light will illuminate for approximately 2 seconds to check that the tire pressure monitoring system (TPMS) ...