Make: Projects

Radar Speed Detector

Turn a Hot Wheels toy into a versatileradar gun.

radar speed detector opener

I was browsing through a department store one day, in search of a gift for my 8-year-old daughter, when I came across Mattel’s Hot Wheels Radar Gun ($30). The box said that this toy could clock the speeds of not only miniature Hot Wheels cars, but also full-sized vehicles.

I figured the toy must have severe limitations, but decided to buy one for my daughter anyway. It turns out that she (we) loved it, and we found that it could accurately measure the speeds of toy cars, cars on the road, even joggers. To my amazement, the detector even measured the speeds of spinning objects like bicycle wheels.

Operating the toy is simple: you aim the gun, squeeze the trigger, and then read the detected speed on the LCD in back. Hold the trigger down for a while and then release, and you’ll get the maximum speed detected during that time. A switch selects either mph or kph readings, and another switch toggles the display units between 1:64 scale (for Hot Wheels) and 1:1 scale actual speeds. Power comes from 4 AAA batteries housed in the handle.

Inside, the Mattel gun uses Doppler radar, just like the expensive speed detection systems used by law enforcement. It transmits a continuous wave at 10.525GHz, then measures the frequency that returns after the wave bounces off a moving target. The main functional difference between the Mattel toy and a $1,000-plus pro model is detection range, which for the toy maxes out at 40 feet. I suspect that this keeps the microwave emissions low enough to guarantee child safety.

Limitations aside, I realized that this so-called toy offers some interesting prospects. The wheels in my mind began to churn, and I decided to purchase another unit for my own use. I disassembled the gun and decided to repackage it to appear more professional — looks really are everything.

I separated the detector component itself (the waveguide antenna) from the display and control panel, then connected the two with a length of instrumentation cable. This configuration lets you position the antenna close to traffic on a tripod, and operate it remotely from a safe distance.


Step #1: Disassemble the toy.

Radar Speed Detector
  • Disassembly is no easy task, as there are 12 screws, each concealed with plastic inserts. I used a drill and ¼" bit to carefully drill out the inserts and gain access to the screws. Use extreme caution with the drill, since some of the screws are located very close to sensitive internal components.
  • After removing all the screws and opening the case, you’ll see the long, cylindrical waveguide antenna and a small circuit board that carries the buttons and LCD panel. (The waveguide is a hollow tube that surrounds the microwave antenna and directs and concentrates its signal.)
  • After recording their locations so you can reattach them correctly later, unsolder all the wires that connect the waveguide, battery compartment, and trigger switch. Be careful when working with the waveguide, which is made of a thin, dielectric material and dents easily. After detaching all the wires, remove the waveguide and display panel, and set them aside.

Step #2: Part I - Upgrade the antenna housing.

Radar Speed DetectorRadar Speed DetectorRadar Speed Detector
  • For the waveguide antenna housing, I chose an “Ice Tube” by Alvin. I’ve used these 3" diameter acrylic document tubes in previous projects, and I like them. First and foremost, they look cool and futuristic — transparent with various tints. They’re also fairly rigid and you can easily cut them with a hacksaw. I used transparent green tubing and cut an 8¾" length.
  • For a post that holds up the housing and makes it attachable to a tripod, use a ¾" diameter threaded PVC nipple, 8" in length. Drill a ¾" hole in one end of the acrylic tube and insert the nipple through it. Then screw a shrub sprinkler head onto the end of the nipple. Just below the sprinkler head, drill a ¼" exit hole to route the cable through.
  • Secure the sprinkler head to the wall of the tube opposite the hole, using the screw that came with the sprinkler head plus 2 smaller screws on either side to prevent rotation. For these, drill 3/32" holes through the tube and head, and apply two 1"×¼" sheet metal screws.
  • To secure the waveguide centered inside the tube, use 12-gauge steel wire, carefully wrapped around the waveguide in a spring-like fashion to form 2 mounts, one at each end. Pressure and friction on this wire are what holds the waveguide in the tube housing. There are no screw attachments.

Step #3: Part II - Upgrade the antenna housing.

Radar Speed DetectorRadar Speed DetectorRadar Speed Detector
  • Before inserting the waveguide with mounts into the housing, solder on a new, longer interface cable that will support remote operation. The toy originally used a 4" length of shielded 2-conductor cable, so I figured that the new cable should also be shielded.
  • In my garage, I found a 20' length of instrumentation cable with shielding. Cut and strip one end of the cable, and solder 2 of the available 4 signal wires to the signal contacts on the antenna’s round printed circuit board. Also solder the uninsulated drain wire, which connects to the shielding, to the board’s ground contact in the middle.
  • Route the opposite end of the cable through the waveguide housing and PVC nipple, and then carefully push the waveguide assembly into the housing. To attach the housing to a camera tripod, remove the tripod’s head assembly and support tube from the base, then route the antenna cabling through the hole, and slide in the PVC nipple and waveguide housing.
  • The other end of the cable would attach to the display, but I wanted to make it easily detachable for transport. So I obtained a 5-pin DIN male connector plug and matching jack. Solder the 3 conductors that were connected at the other end to 3 contacts on the DIN plug.

Step #4: Part I - Build the display housing.

Radar Speed Detector
  • To house the radar detector’s display and controls, originally on the back of the toy gun, I used a 6"×3"×2" project case. First I made a carrying handle out of a bar of 0.1" thick steel (aluminum would have been easier to work with).
  • Drill ¼" holes in each end of the steel and bend it into a U shape. Drill corresponding holes in the display housing and attach the handle using hex bolts, nuts, and washers. One of the nice things about the handle is that it also functions as a stand, allowing hands-free viewing when the display unit is on a tabletop or other flat surface.
  • I needed to make a large hole in the lid of the display housing to fit the LCD display panel. Since I didn’t have any large-diameter bits, I used a ¼" bit to make a series of small perforations in the plastic. Punch out the section with diagonal cutters, and file the edges smooth. Then install the LCD panel to the lid by running a couple of 1/8"×¾" sheet metal screws through its 2 original mounting holes.
  • To replace the functionality of the original momentary trigger switch, I chose a double-pole, double-throw rocker switch. This has the advantage of allowing for automatic, hands-free speed measurements. To install the switch, drill a ¾" hole into the display housing lid, centered below the display, and secure the switch in place with its retaining nut. To reinforce the display and switch, you might also add some glue.

Step #5: Part II - Build the display housing.

Radar Speed DetectorRadar Speed DetectorRadar Speed Detector
  • On the top of the display housing, install the female DIN connector receptacle, for plugging in the cable. Drill a ¾" hole into the top of the display housing and attach the jack on the inside using a pair of 3mm×8mm screws and nuts.
  • The original radar gun used 4 AAA batteries. This would be fine for our new configuration, but since there is plenty of room inside the display housing, I decided to go with AAs, which have twice the capacity of their AAA cousins.
  • A quick measurement with my multimeter revealed that the radar system draws about 24mA from the batteries connected in series. This translates to almost 100 hours of continuous use with AA alkalines (assuming 2200mAh each). Install a 4-AA battery holder inside the display housing using double-stick mounting tape.

Step #6: Solder all the connections.

Radar Speed DetectorRadar Speed DetectorRadar Speed DetectorRadar Speed Detector
  • With all the hardware installed inside the display housing, it’s time to solder all the connections. The wires connect to 3 components: power switch, batteries, and the DIN connector for the antenna. For the DIN jack, the toy’s original 4" antenna cable had 3 wires, red, white, and a shielding conductor covered with black heatshrink. Solder these 3 wires to the connector contacts matching the other end of the cable, using a multimeter to make sure you get the correspondence right.
  • The toy’s power switch wiring consists of 4 individual wires: 2 brown and 2 blue. Position and solder these to the DPDT switch, following the same pattern as the original manual trigger switch.
  • Finally, the toy’s battery wiring consists of 2 individual wires, red and black. Solder these directly to the corresponding contacts on the battery holder. That’s it for the wiring. After closing up the case and plugging in the antenna cable, you’re ready to go.

Step #7: Let the fun begin!

Radar Speed Detector
  • I started out by having a family member walk in front of the antenna unit. At a normal pace, the display registered 2 mph, and a more brisk pace yielded a reading of 4–5 mph.
  • Next, I decided to try measuring the speed of a spinning bicycle wheel. The tripod was handy for this test, since it let me focus the waveguide precisely where I wanted. I placed the bicycle upside down on the floor, supported by its handlebars and seat. Then I turned the pedal to get the rear wheel spinning, and I clocked it at a maximum rate of 15 mph. So far, so good.
  • Then it was time for the real test, with actual cars on the road. I took the unit outside near the street and set up the tripod. It wasn’t long before a vehicle came along, and the readout showed 19 mph. That was great — the detector was showing a speed for a passing automobile. But I wondered about its accuracy, so I decided to get into my car and drive down my street past the detector myself. Watching my speedometer, I drove at a steady speed of 21 mph. Heading back to my driveway, I was anxious to see what the device had measured, and to my delight the reading was 21 mph!
  • I’ve done several projects over the years, and this one has been one of the most satisfying. The Hot Wheels Radar Gun has some great hardware inside, and for my minimal investment, I now have a system that provides a useful function that I’m sure I’ll be using and enjoying quite a bit for years to come.


This project first appeared in MAKE Volume 10, page 148.

  • T

    Tell me how a microwave can hurt somebody?

  • kathleen hunt

    Anyone still using – Azon Deal Buster (just google it)? I haven’t been able to see that gold box that gives you a list of any discount for radar detectors. I save big everytime that I use this box, it’s incredible.

  • Bryan Gibson

    Is it possible to connect the gun to something like the Raspberry Pi with a camera kit so that a picture is taken at certain speed readings, say anything over 35mph? I live in a neighborhood with no through streets but it doesn’t stop people from tearing through here…sadly, it’s not all teenagers.

    I’d like to be able to 1) get an accurate speed reading, 2) have a picture taken to capture the license plate number and 3) have the photo automatically emailed to the local PD who can then do whatever they want with the photos. My main motivation is to keep my children from becoming paraplegics.

    • Dennis Piel

      I’m trying to do the same thing so please let us know if you figure out an option for this. Thanks!

      • Bryan Gibson

        Sure thing! I’m new to arduino but I’m sure something can be done with that. I’ll have to seek out a few experts. The programming side shouldn’t be too hard at least.

        As a side note, I’m NOT trying to promote a police state mentality, but I think people need to have an awareness.

    • Aaron Bird

      I recently moved and I have cars flying by 15 – 35 mph consistently over the speed limit which is 25. I would love to get something like this set up. The big thing for me is to provide evidence that it’s actually happening. I would like to set up a database and log the speed, time of incident, license-plate, etc.

    • Ikos Log

      None of this would work. Building your own system and not being an officer wouldn’t hold up legally. For regular speeding tickets there are technical precedents that must be followed by the police and equipment… I would say 99% of the population doesn’t know about these things.. for obvious reasons. At any rate,.. the Guns must be certified, and calibrated regularly.. They also must be checked before and after each shift. If someone were to challenge a speeding ticket and knew how to properly address these issues to the officer,.. they could (and some do) get their tickets dismissed due to the officer not properly testing the gun before and after the shift that day — or the gun not having been calibrated recently.. etc. — This is with $1500-3000 equipment (or more) designed and used by the police.

      Thus, designing your own is fine.. adding a camera or video system would be easy enough… But it certainly wouldn’t (and shouldn’t) be allowed legally to convict someone of breaking the law.. ie: Speeding.

      It still could raise awareness, and provide enough proof for police to set up some speed traps in the area you have issue with on occasion to try and curtail these speeders.

      You know those signs that blink your speed? Well they have Radar guns in them obviously.. and if the city could have people over X limit issued a citation via these they would,.. however because they do not meet the stringent requirements that I speak of above they are simply there to make people aware of their speed.

      On the other hand, there are “speed cameras” often mounted on redlights, or other poles around cities that will send a “ticket” to the person via Mail — Even here it is not in the same category as a Speeding ticket issued by a police officer. The law is very strict on the tracking and methods used to ascertain moving violations pertaining to speed.

      I’m not a huge fan of people who take it upon themselves to “police” others “infractions” — But I DO understand people who GROSSLY drive too fast in residential areas .. not 5 mph over.. but someone going 50mph in a neighborhood.. That is dangerous and should be handled by the police.

      Good luck!

      • Bryan Gibson

        Thanks for your opinion. I’m not a huge fan of people who take it upon themselves to police the internet, so I guess we’re even. I did get a kick out of your one-man point-counterpoint, though…

        I wasn’t trying to use this as evidence in a court of law, issue tickets or make any citizens’ arrests. I am simply doing it for a “state of awareness” as you say. If you read my post, I clearly state that I’m not trying to create a police state, I simply want there to be some recognition of the fact that we have this problem–it’s a closed street (not a through street) and there are children that play in this neighborhood. Besides the fact that I thought it would make a fun experiment if nothing else.

        Also, never ever start a reply with “none of this would work.”

    • Spooky Jonz


      Setup a VCR set to extra long play record time like 6 hours or so. You can get them at local thrift store. Buy some ELP/VCR tapes from Walmart. Setup a video camera on a tripod aimed at speeding cars. Put this gun on another tripod in the field of view. You’ll have to figure out how to lock the trigger in on position and bypass the batteries to a AC power supply to the house via long extension cord. You’ll also need a small book light to illuminate the gun’s LCD screen in all sun angles for the camera.

      Position the gun several feet in front of the camera to maintain focus in the foreground while still zooming the camera to the front or rear license plate (rear would be better in all states). Fix zoom and focus and leave in place. Use your car as the guinea pig. Make sure your car is exactly where most speeders would be.

      One problem is site security. Put it near your house on your property. Watch it closely with another CCTV camera from your house. Put a plastic wide-gap chicken wire fence around it (metal will reflect the microwave signal). Lowe’s and Home Depot sell it. Better yet put in weather proof plastic or wood boxes with the camera with a hole for the lens. This will disguise your rig.

      Put up a sign that says SLOW DOWN AS IF YOUR CHILDREN WERE PLAYING HERE. SMILE YOUR ON CAMERA! Not only will people slow down not knowing what the real deal is, if they have a radar detector it will go off. Even the new laser detectors still monitor this band in case of old fashion sheriff departments with low budget equipment radar guns.

      Now during playback use the visual fast forward feature (I think it’s called jog feature) to watch the LCD display go through several speeds until you see one that is too fast. Rewind and playback at normal speed. If you capture this to your PC you could email the speeder’s license plate to the local sheriff’s department. Big city cops would just delete the email.

      The ideal system would be a PIR (passive infra red) motion detector wired to a relay that would activate the record button and the trigger on the radar gun. That way you would eliminate hours of no cars or bunny rabbits and other animals crossing the road on the tape. Position the PIR several hundred feet down range via speaker wire to allow for time for the VCR to get up to speed as the speeding car approaches or goes by. Aim it the other way so the PIR will stay activated for a while and still see the hot exhaust of the car. Also set the PIR’s time delay dropout to maximum.

      The Radar Gun needs no hole in the front of the box as microwaves can penetrate plastic, wood, or cardboard. It only needs a hole so your camera can see the LCD display from the rear of the box. No box needed for the PIR. It will be nicely hidden on a wooden fence post. You can bury all the wires a few inches down or use PVC conduit to avoid squirrels and other rodents from chewing on them.

      You may have to install a triggered spotlight (triggered by PIR of course) or use a night-vision camera for dusk to night-time recording. Make sure the spotlight is aimed for center road right at license plate level. Don’t aim the light at oncoming traffic. It will scare the bejezus out of people too. You’ll need a dedicated few feet of frontage property for all of this to work well. Hopefully your own property.

      All this typing and I totally forgot that Walmart sells a Animal Trap camera with PIR motion detector for under $100 bucks in sporting goods. Just strap this to a fence post and aim it at your radar gun LCD too in foreground. You should capture the cars and the speed on same image or video. Keep the receipt so you can return it if experiment is a big fail. :-)

      P.S. – I’m just brain dumping here (brainstorming): There is freeware software to monitor a webcam placed by the road and highlighting the area of the road you want to detect motion and start video or still image capturing (Checkout Toucows dot com), Of course you would either need to position gun in front of webcam or run two webcams; one for radar gun. Syncing would be a problem there (how about live OCR decoding of LCD display to text for a Javascript app?). Also you would need very long USB cables if you were not going wireless like through a cheap IP camera.

      Oh I just remembered: if you live on a dirt or muddy road you can forget about capturing anything UNLESS you use your garden hose to keep that dirt road patch wet. That will hold down the road dust.

    • HeatXfer

      Paint 2 marks on the street 40′ apart that you can see clearly from your house or other vantage point. Video tape vehicles as they pass over the marks. Just record the time it takes a vehicle to travel from one mark to the other and then calculate from feet per second up to mph. (5280ft/mile). Show your findings to the local PD and ask they monitor the street in an unmarked car.

    • lightmanca

      Hi. Did you get anywhere with this? I want to set up a speed “trap” that tweets offenders. We have no sidewalks, and I’m tired of people speeding on my street. Maybe if they are recorded on twitter it would help.

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  • Antennas

    What you really need to do is set up two sensors that people drive over. Those long black cords that you see in the road. Then it is simply a matter of time vs distance. Then you can calculate speed with an accuracy of near 100%. Have a camera snap a photo and send it to your email. Then take it in to the local PD and see what they will do for you. In Canada a ticket can be written on a citizens complaint. You need to go to court if they fight it though don’t forget.
    As for your radar gun needing to be calibrated, that is only partly true. If you bought a tuning fork and used it you would be fine as you could show that it is correctly measuring speed. BUT for 10.25 GHz I don’t think you would find a fork for that frequency.
    Ask for increased enforcement on your street and keep calling. Squeaky wheel gets the grease!!

  • RatedProductReviews

    Whats the best radar detector on the market? Find all about them at

  • Radar Detectors

    Operating the toy is simple: you aim the gun, squeeze the trigger, and then read the detected speed on the LCD in back.

  • Radar Detectors