Need to build a dummy car alarm with bright-red flashing LED

November 15, 2016 7:50 AM

Someone recently broke into my car at night. I can't afford to install a true car alarm. Instead, I'd like to put a bright red flashing LED on my dashboard.

I already bought this device and this one. They're both of very low quality, and the LEDs are much too dim (you can barely see them). I would like to build my own fake alarm.

I'm guessing I'd need to start with LEDs like these, correct? What else do I need to do? I'd probably need some kind of small box to hold the battery and a simple on-off switch. And maybe a light-sensitive switch that turns on the LED in darkness -- though I can probably live without the light-sensitive switch, if it's too complicated to make this work.

You can assume that I have basic soldering abilities, but not much else. As a kid (40-some-odd years ago), I used to tinker with P-Kits from Radio Shack. That's about the extent of my electronics experience.

posted by akk2014 to Technology (6 answers total)

Best answer: The simplest thing you can possibly do is an LED throwie with, as you said, a flashing LED. No soldering required, and also, no switch.

You can probably see how to throw a switch and a battery holder into the mix.

Next step up is, I guess, running the LED from the car's battery, and after that have it run only when the engine's off.
posted by Leon at 8:35 AM on November 15, 2016

If you want, you could also go to places like Dollar Tree and Five Below that have cheap electronics -- the FM transmitter I got from the latter has a bright red LED. You could pull stuff out of its case and have it already made.
posted by fiercecupcake at 8:37 AM on November 15, 2016 [1 favorite]

I actually had this done by a car stereo installer on my (2003) Elantra. I was having a stereo installed at the same time, however, so this might not be cost effective to have it done solo. However, the installer used one of the blank switch plates on the dash (where a switch for an optional feature would be) and wired it in to the car's power so it only blinked when the ignition was off. The car did actually have an alarm but no flashing LED. :-)

I should mention that the car was still broken into... twice.
posted by kindall at 9:30 AM on November 15, 2016 [2 favorites]

You can build a LED flasher that will run approximately forever off a car battery using just five components including the LED and the power switch. Use the fixed resistor + variable resistor combination shown in this video to get the flash rate you want for your LED, then substitute a fixed resistor of approximately the same total resistance when you build it up for use in the car.
posted by flabdablet at 9:57 AM on November 15, 2016

Yeah, or just use a super-cheap 12V flashing LED... technology seems to have moved on since last time I did this :-)
posted by flabdablet at 9:58 AM on November 15, 2016

I don't think that a blinky light will make the slightest difference. The only car security systems shown to make a difference are those that disable the ignition, and that only prevents theft of the car, not theft of the contents.

Can you get renter's or homeowner's insurance to cover stolen contents, and maybe better car insurance to cover damage to the car? It's frustrating to have no power to protect your car, but maybe you can protect your longer term financial condition.
posted by Capri at 5:10 PM on November 15, 2016 [1 favorite]