Finding my RFID car key

Hi,
all the electronics is hidden under the dashboard or is a part of the car control unit. It communicates with the transponder inside the key when it is inserted in the keyhole and it checks the validity of its response. IMHO it would be the easiest solution to rip the electronics from a scraped car that used a similar type of immobilizer (the same frequency, protocol etc.). It seems to be a bit hard to find its full documentation.

BR from Ivan

Ivan, thanks for your reply.

You have described my plan exactly. I have a spare RFID key for this car.

How do suggest the methods I should use, including frequencies and circuits to create the key finder?

Thanks again.

Hi,
if you can get an old, but still functional immobilizer of the same type, you can detect the key response and make a portable "car key finder". Just a raw idea.

BR from Ivan

Harry, to clarify, I am not looking for a way to enhance the likelihood of finding my current car key if I lose it by adding circuits to it. I lost a key that uses the Immobilizer technology (vintage 2004) in the key and ignition key switch in the car.

Hoping to resonate the key’s tuned circuit at a distance of less than 30 cm using 115-135 KHz sweep with 1 KHz AM and listen for changes in the 1 K tone.

I welcome your observations and suggestions on my approach.

Thank you Harry for your reply. Glad to see you’re out of bed now and your health is improving.

Can you suggest the design of a large coil? Wire gauge, number of turns and diameter? (Not sure what “anti-turns” are—do you mean a pair of wires joined at one end and in parallel wound into a coil, and the 2 free ends used as input to the coil?)

Yes, getting a visible dip may be difficult, that’s why I’m considering using 1 KHz modulation and a detector to give audio output. The ear can detect very small changes that may be difficult to see on a meter or scope.

Thank you again.

This is an interesting topic.

I did a few experiments with RFID and even with car remote keys.

RF key (433.92MHz)
Around 1999 I listened to this frequency, opened my own car and recorded the tones, saved to an MP3 file. I put the file on endless-loop and sent it back with my UHF handheld. It worked. In 2001 it didn't work anymore. Nearly all cars have a non-repetitive code today.

RFID
I have loads of these and I have been saving old tags.

Many of the older ones use low frequencies around 125kHz and 134kHz, but the general RFID frequency in common use today is 13.567MHz. I have not found any of these to give a decent dip with a GDO, at least not a dip I can measure at more than a couple of inches.

My Stockholm underground railway cards gives me a good sharp dip at almost 16MHz, but my house-key, company ID card, VISA card and some hotel-keys I have collected do not display a dip. But all of these I can read (not the VISA card) with my RFID card read/writer. The hotel keys and house keys are simple to detect and clone but the railway card and ID card I had to download some SW to be able to read them as they were encripted.

My card reader works about 4-5" from the cards, but most door locks need to have the key about 1" or less to open the door. I wonder if you could try using a larger coil? With "anti-turns" to gt a larger coverage area?

EAS
These are the little thingies they hide in knickers, whisky cartons, lipsticks and shoes. When you walk out of the door they set off all manner of bells, whistles and klaxons. These seem to work about a metre, and I can detect them with my GDO at about 15cm (6"). They are a Hi-Q tuned circuit at (usually) 8.2MHz, and yes, you CAN set the alarm off with GDO tuned to 8.2MHz (even if it is switched OFF).

There is no logic in them since they are always destroyed in use (to disable them), so they are built to a low price. They are ony a tuned circuit, which is why they give a good response.

If your GDO was built with a larger diameter coil then it could cratainly detect these things at more than 50cm. Perhaps you could make up a few of these things and nail them (or glue :-) to your key-fob? Just avoid 8.2MHz or you will always have a problem trying to leave H&M, BHS, AZDA, ICA, Mothercare etc.

So to answer your question, RFID tags are not normally easy to detect with a GDO. You can supplement the key with another type of RF tag that is more easy to detect with a GDO.

FFT (Food for thought)
If you can make a tuned-circuit you can glue to your keys, then you could use one with two coils and a diode coupling them. The second coil being 3x the frequency of the first. So if you radiate 20MHz, then you will get 60MHz returned. With a zero-bias schotky diode you should be able to get a decent range.

Have I helped you at all?

Best regards from Harry - SM0VPO (also EA/SM0VPO)
(been sick, bedbound, for a few days)

And I have a spare key to experiment with.

I’ve been recommended to build a GDO to resonate a missing car key at a distance of about 12 in (30 cm). There is metal in the area so a metal detector or magnet won’t work to find he key.

The immobilizer circuits in car keys (this is a traditional key with RFID chip, not a proximity fob used in the modern “push button start” cars) of the 2004 vintage work at 125 KHz. I’m told that a GDO is a good technique to find a RFID circuit. I’m also told that modulating the signal (1 K) and putting the output through a detector and amplifying will give a sensitivity the ear can hear, better than can be displayed on meter or scope. (As well, this all needs to be portable and small.)

Any suggestions are welcome.

Thanks.