A cop in every car

[Michael] designed this display board to mimic the appearance of a police car pulling you over. It resides in the rear window of his car (facing forward) as the controller board measures the speed of the vehicle. An Arduino grabs NMEA data from a GPS module and compares it with a table of speed limits. If you are speeding, based on your current location, the reds and blues flash as if you’re getting pulled over. The thrill of getting busted for a lead foot doesn’t sound like much fun to us but to each his own.

Incidentally, [Michael] is using the EM406 GPS module, the same one as the Frustromantic Box used.


  1. unsupported says:

    Having red and blue lights in a vehicle is illegal in most, if not all states.

  2. fenwick says:

    I was about to say what unsupported said. In my state, they’re illegal if they can be seen from outside of the car

  3. Rufus T. Harlemberry says:

    I will be putting one of these in my daughter’s car.

  4. fartface says:

    wow dumb…

    Why not just a red blinking light on the speedometer?

    Why is it so many “hacks” are more dorky than useful?

    Let’s push this one further…. if you exceed the speed limit, cut the fuel pump.

  5. pod says:

    sure, but these are facing forward and small enough for you to be the only one noticing them (except at night)

  6. Haku says:

    Despite the red/blue light laws it’s a neat idea, though I would have put the LEDs on the same board as the microcontroller+GPS instead of trailing two CAT5 cables to the back of the car.

  7. Codewar says:

    This is a horrible idea! You’ll get pulled over trying to use this thing!

  8. Digital says:

    I used to have a plethora of cathodes in red and blue in my car. Got a lot of people out of my way when I was in a hurry, but one day I got slapped with a $250.00 fine. on the other hand though, these are very small and I very much doubt that anyone outside the vehicle would confuse these. And what if you had a dvd playing on one of those portable players and it had red a blue flashing colours for whatever reason, would there be justification for pulling you over? if it’s just a brief burst I don’t think it would ever be a problem.

  9. Michael says:

    Good points about the laws regarding red/blue lights. But this isn’t really visible outside the car. The LEDs point forward. During the day, the LEDs just aren’t bright enough to be seen by a car in front of me (yes I did some testing). At night my own headlights are bright enough to drown out little LEDs.
    This isn’t a really practical project — just for challenge/amusement.

  10. BiOzZ says:

    its illegal in the usa to have red or blue lights inside the vehicle that is viewable in any way outside the vehicle (day or night) and you can be charged with illegal vehicle modification and in some cases felony impersonating an officer

  11. JAGAK says:

    Oh man, any one else want to post on legality, cause i don’t think any of us get it yet… Now what would be real cool is to have this mounted in the rearview mirror like the ones that display temp, direction etc.

  12. jamieriddles says:

    “Let’s push this one further…. if you exceed the speed limit, cut the fuel pump.”

    How about a taser that shocks you for speeding?

  13. Boudico says:

    Neat idea. Regardless of the legality issues implied. If I understand the workings correctly, you could fairly easily modify this to be completely ‘legal’ and ‘fuzzily happy’ to most people. How? Have it compare the mph against the table as you do already, but instead of flashing lights, have it log it to a file with mph/time/date/loc/etc that gets appended each time you ‘speed’. Then, mom/dad could d/l the log and see what junior/juniorette has been up to.

  14. carl jones says:

    Why? Because it’s funny and creative. This blog is Hack-A-Day — not Law-A-Day.

  15. Whatnot says:

    So if you boost this and install it in the fender you automatically become a fake cop when you exceed the speedlimit, handy that.

    Or more legally what he should do is make a plug for real policelight to plug into and then sell this to policeforces so they have automatic engagement if they need to speed, he can make a bundle.

  16. MrDan says:

    “Having red and blue lights in a vehicle is illegal in most, if not all states.”

    “its illegal in the usa ”

    You people do know that there are other places than the USA, right?

  17. JaB says:

    Everyone is somehow worried about the red and blue lights being illegal, but somehow nobody seems to point out that speeding, too, is illegal.

  18. bzroom says:


    preach brother.

  19. asv says:


    Forgot it had to be legal to be fun!

  20. Buzzkill says:

    Awesome HAD project. Creative use of the GPS module +1. If it were just the red and blue lights I would have said “meh”, but the fact that you also added the white LED’s to simulate the headlights is +1. Doing it “just because” is +1. Documentation, schematics, and posting the code, also +1.
    As far as legality, whatever. There are so many stupid laws on the books anymore, all of you whinners probably broke a dozen laws before you finished breakfast this morning and didn’t even realize it. But some of you did, and we know who you are.

  21. Dave says:

    As a precursor to the fines for both speeding and use of red and blue lights, the passenger in the car will hear “Hey, watch what happens when I…”

  22. Sashimi Cat says:


  23. LordDominoTwain says:

    For all the “it’s illegal” folks… you’re missing the point. If the lights are on, you are already breaking the law — this just adds some gravy to the deterrent.

    But, if you really want to Pavlov yourself into a model citizen, throw in bluetooth connectivity and have it *77 highway patrol with your location, speed and license plate number. As a bonus, that’s probably illegal as well.

  24. BiOzZ says:

    speeding = misdemeanor
    impersonating an officer – felony

    speeding – ticket
    impersonating an officer – you car is seized and you face up to a year in jail

  25. Megan says:

    I think this is a dumb idea! First off, who wants to deal with the annoyance when they are going a little fast. Have we really become that pathetic that we want a speed nanny! Secondly, if you really need such a ninny device, just put a warning light on the gauge panel. And finally, any parent who would actually put this on their kids car is lame and a square. Stop trying to be such an overprotective parent. Why not instead be a better parent and raise a better kid?

  26. ejonesss says:

    i am not sure how legal that is.

  27. BiOzZ says:

    i think a better hack would be a police radar detector or a cop detector or a GPS based speeding camera alarm

  28. VIPER! says:

    They have these integrated into normal speed limit signs at fort Rucker Al. They really freak you out until you realize that’s its a sign flashing red & blue and not a cop. Its a very effective reminder, you DO NOT want to get caught speeding on BASE.

  29. LoBo says:

    This is what I see happening: You get used to having this device installed in your car and start ignoring it. A real cop tries to pull you over > High speed chase. :)

  30. Michael says:

    I’m glad at least some HAD readers think my project is interesting or humorous. For all of you with the legality comments — yeah, I *get it* — it’s illegal to have the red and blue blinkenlights in the car. This wasn’t installed permanently – just for a few days. I drove around one night with my son and we had a great laugh.
    All you wannabe lawyers — sheesh, I bet you’re real fun at parties.

  31. anon says:

    You can always count on Hack a Day posters to beat a dead horse.

  32. Mike says:

    Hey fartface-lets do cut off peoples fuel pumps. I’m sure that will be absolutely genius on I25 during rush hour when everyone is doing 80. One guy all of a sudden slows down because his fuel pump shut off and you’ve got 3000 cars piled up in a big tangled mess behind him.

  33. Mikey says:

    This sounds unsafe and possibly illegal. What is likely to happen is he will eventually ignore the leds because they will be such a common occurance that he will ignore cops trying to pull him over as well thinking they are the leds.

    Also what is likely to happen is if he is speeding and a cop is behind him, trying to pass with it’s lights on, he will not notice the difference in his peripherial vision.

  34. DeadlyDad says:

    Ummm…guys? Imagine you are a state trooper, and you pull some guy over because you notice a dim, flashing blue and red glow in his back window. Once he explains that it is a simple hack to warn him that he has gone over the speed limit, would you be more inclined to arrest him, or give him a pat on the back? Personally, I like it, especially if it was made completely portable and you tossed in the back window of a buddy’s car; as soon as it went off, his first reaction would be to hit the brakes, dropping his speed and turning it off. This would probably happen fast enough that he would have already dropped back below the limit before he had a good look in his rear-view mirror…where no patrol car exists. He would most likely catch on after a couple of times, but, until then, a hidden dash cam would make for an /awesome/ YouTube video!

  35. soopergooman says:

    gps speeding alarm, built in psp homebrew Mapthis/mapViewer, this will get you BUSTED BY REAL COPS. basically this is called IMPERSONATING AN OFFICER. Those lights will not only mimic being pulled over but in MOST COUNTRIES it’s totally illegal. What about the drivers in front of you. They see this and BAM they call the real ones on You.

    I say BUILDER BEWARE!!!!

  36. soopergooman says:

    side note, maybe you coulda hooked this up to a computer game to mimic when PRETEND COPS are coming to get you. It’s a nice hack but maybe just an AMBER Light would just as good. You say “You and your Son had a great time with it a couple of nights” Quote: “. I drove around one night with my son and we had a great laugh.”
    Soooo You yourself have just confessed to Impersonating an Officer of the Law. Great role model your presenting yourself to be.

    We like hacks that do good not bad….

  37. RBRat3 says:


    yea and when i was 5 i wore a sheriff badge with my name on it so i suppose i was impersonating an officer. On a side note its only 8 led’s and are probley no brighter than the inglows for your red and blue temperture knob/slider indicator.

  38. Birdman says:

    This guy came up with something creative to help him stay safe while driving and it seems like everyone is just putting him down with these ‘legality’ issues…

    I don’t think he deserves it!

    I mean, you all know that normal LEDs aren’t bright at all! How would someone outside the car even be able to see this?

  39. Michael says:


    Wow, get a grip.
    When I was testing this out, if there were any other cars around (oncoming or behind me), I just pressed the test button to turn off the lights if they were on. I really didn’t want others to see them, even though they aren’t bright enough to fool anyone into thinking I was a police officer or something. Sheesh.

    I wasn’t “Impersonating an Officer of the Law”. I like how you capitalized the words to emphasize the gravity of my heinous crime.

    > “Great role model your presenting yourself to be.”
    Yeah, doing electronics projects with my son is soooo evil.

    Glad you’re policing the internet for us — we all feel safer. Hang in there, kid. You’re gonna make detective some day!

  40. sarsface says:

    HAD–Best comedic website ever.

  41. anthonydi says:

    Make the car twitter you when your speeding.

    I doubt this thing would be bright enough to get you in trouble.

  42. JAGAK says:

    Wow, after an entire day of one legality post after another & people bashing the wannabe cyber police for doing so repeatedly, people are still pointing out the obvious. HAD trolls are out in force and just as dim as the LEDs in this project. Seriously its not like he is using Luxeon or Cree LEDS… I’d expect more from HAD readers. The laughs gained were undoubtedly derived from glee in seeing their project worked and not from “illegally flashing lights in their vehicle” as much of a thrill as that would be I’m sure. Get mad and bash more creative thinking and just for fun projects because you don’t have the brain power to pull it off, or… before you get a chance to retort go make something better and post it else stfu & gtfo, thx bro!

  43. Life2Death says:

    Not true, if blue leds were so dim as you say they are there wouldnt be 500 posts on every computer case using them that “the blue leds are too fking bright”

  44. Bill "Smith" says:

    This is a good hack. While its true that the blue lights can get you pulled over its usually the meth pipe that gets you in trouble.

  45. strider_mt2k says:

    The legal nuts are…crazy.

    JAGAK – +1

  46. Timmy says:

    I don’t think this device is about the lights. It looks like the builder wanted to demonstrate how easy it is to have a device put into a vehicle that could monitor speed without having to connect it to the vehicle’s speedometer, and alert authorities to the fact that it’s speeding.
    This device is likely intended as a warning to us how easy this is, and to be on the lookout for lobbyists or legislators pushing to have such a device installed in every vehicle, ostensibly to protect us from speeders, but in reality, to provide an excuse to monitor everyone’s location.

  47. Pilotgeek says:

    Everybody whining about Red/Blue light legalities: All I ever hear in the comments anymore is-
    a. Not a hack
    b. Something about the legality.
    c. Something about safety.

    Since when do hackers give a crap about safety and legality? Christ dudes, live a little.

    • komodo says:

      that bring me to ask when did it torn from modding hardware/device. to hacking.

      or even calling putting twine on the back of a monitor to hang on the wall a hack when its not.

      is hacking not involving breaking software code any more?

  48. blackman says:

    I made something like this ages ago with a mate for his shoes, it was just 555 and a decade counter with a few diodes. It only flashed the lights to mimmic cop lights. One shoe was a racecar, the other was the cop. Indicators headlights and all :D

  49. Jess says:

    Id like to see this done in a much smaller package, and with suction cups. That way I can sneak it into the back seat of a buddies car :)

  50. Scott says:

    At least it doesn’t use Arduino. Oh, wait… [scratches head]

    If the technologically-challenging part of this project is making a GPS unit talk to a microcontroller, why is the photo of a few resistors and LEDs? Very disappointing.

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