A turn signal is a blinking light that tells other drivers what you intend to do. It sounds trivial. It is one of the cheapest and most effective safety devices on a car.

Early cars used hand signals. Flashing electric signals appeared in the 1930s. Buick offered them as an option in 1939. By the 1950s, they were standard equipment. The familiar tick-tock sound comes from a thermal flasher relay that heats and cools, opening and closing the circuit. Electronic flashers now make the sound artificially or omit it entirely.

Signal colors and rules

• Amber is the standard color in most of the world.
• North American cars often use red rear signals combined with brake lights.
• Self-canceling mechanisms turn the signal off after a curve.
• Lane-change signals flash three times with a light tap.
• Failure to signal is a primary traffic offense in many jurisdictions.

Some drivers treat the turn signal as optional. That habit causes crashes, especially at intersections and during lane changes. Modern cars can read road signs and camera data to remind drivers, but the responsibility remains with the person behind the wheel. Use it before every turn and lane change, even when no one seems to be around. The one time someone is there is the time it matters.