The clicking of a turn signal ranks among the least-annoying sounds a car can make. Along with the flashing bulb behind the arrow in your car's dashboard, the gentle, rhythmic tick tick tick-ing tones are a sign that your blinker is working properly when you switch it on. Even as technology has progressed, this feature has remained a constant throughout generations of vehicles—or at least that's how it appears to drivers. According to Jalopnik, there's one thing that has changed, though: the actual source of that familiar sound.
The flashing turn signals began appearing in automobiles in the late 1930s when Buick made them standard in some models. Traditionally, the clicking sound is made via heat. Drivers would switch on their blinker, and the electricity would heat up a bimetallic spring in the car, causing it to bend until it made contact with a small strip of metal. When these two components connected, a current would pass through them and power the electric turn signal lights. The bimetallic spring quickly cooled down and returned to its original form, turning off the light, before the whole process started again to create a new flash. As the spring bent back and forth, it created a clicking sound.
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The next evolution of turn signals used a similar trick, but instead of moving a spring due to heat, it sent the electronic pulse to an electromagnet via a chip. When activated, the electromagnet pulled up a metal armature and disconnected the current powering the light (or the opposite, depending on the relay setup). Without the pulse from the chip, the electromagnet turned off and the armature returned to old position and bridged the circuit providing power to the bulbs. As was the case with the thermal spring, the relay clicked every time it moved.
Up until recently, this was how most car turn signals functioned, but things have changed as cars have become more computerized. Many car manufactured today rely on computer commands to activate their turn signals, skipping processes that once produced the distinctive clicks. But the clicking sounds are something people grew up with, and drivers might be unsettled if they heard nothing after activating their blinkers. That's why the mechanical sound still exists in the computer era—even though in many modern cars, it's actually just being broadcast through the vehicle's audio system.
For a visual of how electronic flasher signal systems work in cars, check out the video below.