I noticed that when I activate the turn signal of my 2017 Jeep (full of computerized electronics), the flasher makes a very mechanical sound, just like cars have done for I-don't-know-how-many decades.

These days, you don't need mechanical relays to switch current; semiconductor devices can do the job, and do it with far greater reliability and longevity.

This left me wondering: do even the latest cars still use electromechanical flashers exactly as they have done for years and years, or is the sound coming from a device which is merely there to make the noise, while the lamps are turned on and off by transistor switch?

2 Answers 2


In my car the indicators are controlled with solid state electronics and so could switch silently as there is no relay or bi-metallic strip contactor to make a noise as they are activated. There is however a clicking sound that is produced from the vehicle speakers to provide an audio feedback that the indicators have been activated both to give confidence that they are working and as a reminder to turn them off once the manoeuvre has been completed.

  • Agreed - a lot of vehicles where the electronics are remote from the driving position (e.g. buses, trucks) have buzzers or beepers to create the audible warning.
    – Nick C
    Commented Mar 6, 2018 at 11:25
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    Most (all?) General Motors vehicles since 2008 route the turn signal noise through the stereo, which plays the clicking sound via the driver's speaker. Commented Mar 6, 2018 at 13:30
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    @EricHauenstein I found that rather incredible, but it appears the "feature" is found on some of their vehicles with OnStar (see discussion at gmtruckclub.com/forum/threads/…). Apparently this ensures you can't simply put in a factory stereo and disconnect the OnStar without losing your instrumentation audio too, and requires an adaptor when installing a new sound system. I'd like to think Hanlon's razor applies here but I don't fully accept it [nobody on the design team saw this as a bad idea?]. Commented Mar 6, 2018 at 13:52
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    @DarrenRinger I can confirm from personal experience that vehicles that did not have Onstar installed (maybe it was a higher-trim option) also used this method. In my case the factory speaker itself broke (!?!?!) and had to be replaced in order to restore sound. Commented Mar 6, 2018 at 18:35

In the old days, the flasher used to be controlled by a little device that contained a bimetallic strip. When current was supplied to the flasher lamps, the strip would heat up, bend and turn off the lamps. The bimetallic strip would then cool down and reconnect the power. This process repeated creating the flashing lamps. The bimetallic strip switching on an off created the clicking sound.

Today, the timing of the flashers is controlled by a computer. The computer switches on and off a mechanical relay, which in turn powers the flasher lamps. This relay again makes the familiar clicking sound.

Modern electronics could replace the relays used in cars, however, relays are cheap, very rugged and easy to replace when faulty, so they continue to be used.

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