Browsing all articles tagged with 433mhz

Recently, I’ve seen a number of posts on Facebook groups for South African communities about people having their car remotes jammed and the contents of their cars cleaned out while they are at petrol stations, malls and other public areas. It seems to be on the rise as an easy way for criminals to gain access to vehicles usually to look for high resale items such as laptops, cameras, wallets and purses. This is just a post on building a really simple, not start of the art way to determine if someone is constantly transmitting (jamming) on the frequency cars commonly use for their remotes.

Car jamming works on a very simple process that you simply block the “lock” signal being sent to your vehicle. People often will walk away from their car and press the lock button assuming it will just work without physically confirming this. Essentially when you press the button on your remote your remote sends out a signal that when your car decodes it and verifies it as from your remote will perform an action. Most remotes for cars (and gates/other consumer devices) work at 433mhz. What a criminal will do is simply hold down the button on another remote (such as a gate remote) and this will stop your car from being able to properly receive that signal. An easy way to think of this is that your remote is shouting out a series of numbers that your car can understand. But when another person also presses their remote its like two people shouting at the same time and the car cannot properly hear the series of numbers.

There are a number of ‘detectors’ available but the prices range from about R500 to over a few thousand! Generally these simply determine if there is a signal being transmitted for an extended period of time, and if there is it will sound an audio or visual (usually LEDs) alarm.

Having worked with 433mhz transmitters and receiver pairs for some of the research I did previously on bypassing car remotes as well as building the zacon badges I thought I would give it a go to build a very cheap passive ‘detector’. I put detector in quotes because it still needs a person to visually see the alert!

Essentially you can buy a very cheap 433mhz receiver ( usually they are sold in pairs of receiver and transmitter ) for about $1-2 (~R20). The additionally components you would need are a 5v voltage regulator, a resistor and an LED. You can then wire up an LED to the data channels of the receiver and everytime there is any activity in the 433mhz (and 434) range the LED will come on. Thus if you are trying to determine if there is jamming around you will see the LED staying on.

The circuit is dead simple and shouldn’t take more than a few minutes to build (and should be easy enough to show your kids how to build it too!):


Fritzing of remote jammer detector


Here are a couple more pics of the device:





The ZaCon badges were a ton of work on the hardware side (see ZaCon V Badge [1/2]: Build Time), however they provided their own challenges on the software side as well.

Since my knowledge of chipsets only extended to the Arduino the badges are essentially a complete Arduino without the UBS->FTDI breakout. This means that each badge includes an Arduino bootloader which is _really_ nice if you are coming from an Arduino background or simply have an Arduino and want to play.

The idea behind the badges was that they would provide a means of tracking communication between individuals at the conference. Additionally I wanted this information transmitted to a central location so that it could be stored and visualised (yes yes, Maltego and all). Additionally because people would be moving around I needed to create a ‘mesh network’ of sorts so that anytime someone came into range of any other badges they would be automatically be part of the network. This blog entry is going to cover how the badges did this and the challenges faced, if you are not interested make like a heartbleed and go away.

Eye Candy:

Here is a video of a few of the black badges communicating to each and flashing for all the valid messages received:

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