I am interested in a way of how to open the caar's doors with a microcontroller device's extension hardware (I have an Arduino Uno Rev 3). I know that the key can do it as well but I want to program things. The frequency of the signal is 433.92 MHz and the modulation is FM and AM. Therefore I need a device (a hardware that can be connected to the microcontroller) that can emmit/send and receive signals with this certain wave's frequency.

It is to be mentioned that, for me, it is not the most important thing to finally get to open the vehicle (the central locking system) but to work with it and to do experiments and to read what the key sends (this is actually the most important thing).

Can you recommend a hardware that can read 433 MHz signals ? Are there differences among them?

I want to express my interest into that I want to receive the signal that is sent by the remote key.

(edit) Later on, I can try to get some useful data out of the signal.

But, for the beginning, where do I know that all the remote keys work with the same method (I refer to this Wikipedia article: method of modulation). And this is what I meant with FM (frequency modulation) as an example.

By the way, ATA5811 sounds really good - I read the data sheet and it can use both ASK and FSK (modulation). How can I find out, what my car key uses (there are so many paramters!) ?

  • \$\begingroup\$ please remove the signature and salutation from the end of your post. \$\endgroup\$ Jul 3, 2012 at 20:41
  • \$\begingroup\$ @insta: I did it for him. \$\endgroup\$ Jul 3, 2012 at 20:57
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    \$\begingroup\$ @insta - you could have done it too. It would have taken about the same time as writing your comment. \$\endgroup\$
    – stevenvh
    Jul 3, 2012 at 22:13
  • \$\begingroup\$ What do you mean "the modulation is FM and AM"? \$\endgroup\$ Jul 3, 2012 at 23:28
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    \$\begingroup\$ @stevenvh, Yes, I think Insta did what I have done, which is leave a comment, I find leaving a comment often lets the user know so that the behavior stops, it is not insta's job to do it any more then olin's, you can do it to be kind but you should leave a comment to let the user know to stop. \$\endgroup\$
    – Kortuk
    Jul 4, 2012 at 20:49

3 Answers 3


I think the radio part is the least of your problems. To my best knowledge most car openers use a cryoptographic system called "rolling keys", which means that recording what the keyfob sent and replaying it won't work. Microchip has extensive libraries to go with thier chips intende for this purpose, but you need to sign a non-disclosure to get it. Here is a (probably simplified) explanation.


GNU Radio is an open source software defined radio. You can certainly do your stuff as well as many other radio things with it. The funcube dongle is a cheaper option.

Since the crypto part was brought up: What i assume you want to do is a so-called "replay attack". Very early systems were vulnerable, but current are not (to a significant extend). Today challenge-response protocols, session keys and rolling codes are used to mitigate this attack. The Microchip system is called "keeloq" and was attacked successfully. The radio part is easy, the crypto will be hard.


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    \$\begingroup\$ So I can use FUNcube Dongle to intercept the signal emitted by the remote key for my car ? However, it looks like an USB Stick, but I want something to work with my microcontroller. So, I already have a microcontroller and want to receive 433MHz signals. \$\endgroup\$
    – user10676
    Jul 3, 2012 at 18:49
  • \$\begingroup\$ @Karl i posted some references to get you started with the (harder) crypto part. Once you have that working you can go and you may want to look into the Atmel ATA5811 \$\endgroup\$
    – suha
    Jul 4, 2012 at 12:55

Have you looked into getting the cheapest possible remote compatible for your vehicle, finding the pin outs/specs online, and interfacing it directly to the Arduino board? Let the remote handle all the crypto stuff and send/recieve the signals that the buttons on the remote would normally initiate via keypress.

Not an electronics dude, but that's how I would do it anyway.


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