Key FOB Tester

Discussion in 'General Electronics Chat' started by bwilliams60, Dec 23, 2014.

  1. bwilliams60

    Thread Starter Active Member

    Nov 18, 2012
    722
    88
    Does anybody have a circuit which will allow me to detect the strength or presence of a key FOB signal. If I repair one, I would like to be able to test it afterwards. This would be in Canada if that is of any consequence.
    Thanks in advance.
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,987
    3,733
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
  5. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
  6. Lundwall_Paul

    Member

    Oct 18, 2011
    220
    19
    This may save you sometime. Our VIP/O'Reilly Auto Parts has one on their counter. It is for customers to use, but you may be able to get a manufacture and/or model number from that.
     
  7. bwilliams60

    Thread Starter Active Member

    Nov 18, 2012
    722
    88
    There are several out in the marketplace and that would be easy to do, but I am looking to build one and I figured someone on here in all their wisdom and libraries, might just have a drawing around. Barring that, I may just buy one and reverse engineer I guess.
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    they are usually in the 433 MHz range, a germanium diode across your meter probes should read a few millivolts.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Some years ago Elektor published a simple circuit for a cell phone sniffer, the basic idea could probably be adapted for whatever frequency the key fob uses.

    If the key fob uses 2.45GHz - you could try pointing it at a microwave oven leakage tester just to see whether anything happens.
     
  10. bwilliams60

    Thread Starter Active Member

    Nov 18, 2012
    722
    88
    Is there a device or circuit which can tell you exactly what frequency something is transmitting at?
     
  11. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    Please watch where this is going... Cause this could go towards stealing cars or illegal activity...

    Thanks
    Jay Sr
     
  12. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    Really? How would that work? the operational frequencies of key fob transmitters is not a secret nor is it any use to a car thief.
     
    Dr.killjoy likes this.
  13. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Most car key fobs use a rolling code - knowing the RF carrier frequency won't help you much.
     
    Dr.killjoy likes this.
  14. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    Lol I am Repo Man .. There are alot of cars that use it instead of locks ...
     
  15. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    Use what instead of locks?
     
  16. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    Merc cars come with a fob remote that is used to open a car and start them .. Most cars have a sensor close to the ignition but not part of ignition so if you can break the lock cylinder and send the key code to the sensor then you have working car.. Also how do you think auto start remotes work with a ket fob car or truck...
     
  17. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    I understand how car security systems work. My question to you is; how does knowing the carrier frequency of the remote control key fob assist anyone in stealing a car?

    Furthermore, the sensor mounted around the ignition barrel is a close proximity transponder reader that energises and reads a chip in the key and has nothing to do with the active transmitter part that controls the central locking and alarm.
     
    K3CFC likes this.
  18. bwilliams60

    Thread Starter Active Member

    Nov 18, 2012
    722
    88
    I have to say I'm with blocco on this one. You are confusing two different systems with each other. Chipped keys were an early design security system that started out with different resistor chips in the key. If the resistance wasn't proper, car would not engage starter. Key FOB's today have a rolling code which changes after every initialization of any button on the FOB and is nearly impossible to duplicate. That is why I know I can ask my question and not break any rules. With over one trillion possible combinations, it would be very hard to guess the right code. I just wanted to find out the frequency of some of my FOB's so I could build a device which tells me if I am sending a signal from a repaired FOB
     
  19. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
  20. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    It is impossible to say what is happening here from the limited information given. The vehicle remote controls may have been cloned, we don't know. I guarantee that what the thieves are not doing is transmitting an unmodulated carrier to open the doors.
     
    Last edited: Dec 27, 2014
Loading...