Mysteriously appearing fob...

Discussion in 'Gen 3 Prius Main Forum' started by Alen Kalati, Oct 5, 2019.

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  1. bisco

    bisco cookie crumbler

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    try disconnecting the 12v for a few minutes
     
  2. hill

    hill High Fiber Member

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    same advice you get when you call for PC tech support from a person talking from a Hut on the other side of the world

    .
     
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  3. bisco

    bisco cookie crumbler

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    first question, before the advice: is it plugged in?
     
  4. The Electric Me

    The Electric Me Go Speed Go!

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    Hmm....
    I have to go with BZzap! contention here.
    I have always understood that with keyless entry system the fobs do indeed constantly emit a signal.
    This is why/how some enterprising criminals have been successful in hijacking and amplifying the signal and stealing vehicles.
    It's why there are numerous suggestions and now even purchasable products that create a "faraday cage" environment to conceivably keep your vehicle more secure when you store your fob.
    It's why years ago people kept telling me to buy Altoids to get the tin, and keep my fob in it.
    And yes, I think the constant signal is how the vehicle "knows" you are approaching and turns on the lights.
     
  5. Elektroingenieur

    Elektroingenieur Senior Member

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    Do you have any evidence that the system doesn’t work as Toyota describes?

    The continual signal is the LF signal from the car, not anything transmitted by the key. The attack is to extend this signal so it will reach the key farther away, which then replies by transmitting a VHF signal, which already has sufficient range to reach the car.
     
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  6. fuzzy1

    fuzzy1 Senior Member

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    I have to go with Elektro here. The coin cell simply doesn't have the capacity to support continuous transmission. Nor even continuous reception, but rather pulsed (continual, not continuous) reception.

    All the hijack schemes I've heard about depend on amplifying the low-level signal emitted by the car, boosting it to or re-emitting near the fob, not vice versa.
     
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  7. The Electric Me

    The Electric Me Go Speed Go!

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    Is that how Toyota describes it?
    If there isn't a constant signal being emitted from the fob? Why can you buy endless Fob Signal Blocking Pouches on Amazon? I was under the impression they are designed to block an outgoing signal from the FOB, not block an incoming signal from the vehicle.

    Would seem to me that if the security of the vehicle is maintained by a non-transmitting fob, that only activates once IT receives a signal from the vehicle, those products would be nearly worthless.
    And what would thieves be hijacking and amplifying?
    If it was a signal FROM the vehicle, then even amplified it would still need the response from the Key Fob...that would most likely NOT be in range.

    Plus a quick google search brings me tons of information, some from Toyota including a video from Toyota that say's " When you get within about 3 feet of the drivers door, the Prius senses the smart key ".
    Which would suggest to me that the "Smart Key" or fob is sending out a signal....to be sensed by the Prius. If the fob isn't transmitting anything how does the Prius "sense" the approaching smart key?

    Hey, I could be wrong. But I have labored under the impression for years that the fobs, Prius and any Smart Key, Push Button Start system, worked with fobs that do emit a constant signal.

    I even read somewhere that recommended when you replaced your battery in one of your fobs, you replace it with your back-up fob, even if it hadn't been used, because even though you might have it stored, it was still trying to send out a signal constantly, even if you weren't using it.

    Not saying you're wrong, but I am saying if you are right...there is a lot of misunderstanding about the situation.
     
  8. The Electric Me

    The Electric Me Go Speed Go!

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    Well...I guess I could be wrong.
    Depressing that I could own both a Prius and now a Honda Fit both with keyless entry and push button start and be wrong about the fundamentals of how a core system works.
    You'd think I would of read something before today that explained it better.

    Oh well...not the first nor the last time I'll be wrong.
     
  9. BZzap!

    BZzap! Senior Member

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    How does a quartz watch run for years with a simple button cell battery? How do TPMS sensors transmit for years with a simple button cell battery? I don’t think key fob are any exception given the exceptional low potential that these devices use. Even if the car relays a signal to the fob to activate the dome lights, it still must have a “stay alive” parasitic draw.
     
  10. The Electric Me

    The Electric Me Go Speed Go!

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    Yeah, I'm not sure I am wrong.
    Found this from an article about "how" thieves are stealing SKS cars.

    " Key fobs are constantly broadcasting a signal that communicates with a specific vehicle, he said, and when it comes into a close enough range, the vehicle will open and start. The thief will bring a device close to the home's door, close to where most keys are sitting, to boost the fob's signal. They leave another device near the vehicle, which receives the signal and opens the car. "

    So the author of this article could be wrong.
    But like I said, if I'm wrong, there is a lot of misinformation out there. Because the idea that the fob constantly TRANSMITS a signal is very prevalent.
     
  11. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes; see post #19, with Step 1 and Step 2 quoted verbatim from Toyota’s training course.
    The blocking pouches attenuate both an attacker’s amplified LF signal from the car and the VHF signal from the key. If either signal isn’t received, the attack is prevented, since it depends on two-way communication.
    That’s exactly the problem: the LF signal is not strong enough, without help from an attacker, to reach the key, unless it’s near the car door, but the VHF signal from the key is strong enough to reach the car.

    This is by design, so you can, for example, stand in a building with the key, press a button, and look outside to confirm that that you’ve locked a car parked on the street or in a driveway. It also suggests a possible defense against some attacks, though I don’t know if Toyota or anyone else has implemented it: the key could transmit at lower power when replying to the LF signal, and at its full power only when a button is pressed.
    Indeed, unless the key is in power saving mode, it is always listening for the car’s LF signal, but it’s not transmitting continually.
     
  12. fuzzy1

    fuzzy1 Senior Member

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    Those signal blocking devices work equally in both directions. For products at this level, they generally have no concept of direction.
    Extremely low power consumption. And not transmitting anything.

    Note that the old LED watches, intentionally emitting light, didn't display continuously, but only when a button was pressed. The later LCD watches with continuous display don't emit any light, but just alter the reflection properties of the working fluid. The 'light' is reflected ambient light, or from a momentary internal light only when a special button is held down.
    They don't transmit continuously, but only with a very brief infrequent pulse, like (crudely) once a minute. The listen interval on your fob is far shorter, so that the dome light comes on much quicker.
    The 'stay alive' watchdog timer consumes far, far, far less power than any form of RF transmitter.

    Then the radio receiver, which consumes much less power than any equivalent transmitter, listens only at intervals, not continuously. We perceive it as continuous because the intervals are short, but they still save a lot of power by keeping their operating duty cycle very low.
     
    #32 fuzzy1, Oct 6, 2019
    Last edited: Oct 6, 2019
  13. The Electric Me

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    OMG!
    I'm so confused now.
    I think I've been hoodwinked, bamboozled, and led astray!

    For years I've believed it was the key fob acting as Dr. Seuss's little bird, quietly approaching the vehicle and calling out meekly, "Are You My Mother? " .

    When in actuality it was the vehicle all along acting as Horton hearing a Who.
     
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  14. ASRDogman

    ASRDogman Senior Member

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    I don't believe the key fob transmits a signal constantly.
    The car sends out a signal and activates the fob which responds.
    Same with the TPMonitors.
    I guess it's similar to a remote and tv. The tv responds to what the remotes sends.
     
  15. fuzzy1

    fuzzy1 Senior Member

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    The claim of constant key fob broadcast does conflict with the consensus of very many statements and articles linked in many threads in this forum over quite a few years. Though a quick search does find many generic articles now assuming the constant-fob-broadcast idea.

    Some 'relay attacks' use 2 people to perform the relay. But this Toyota version could be attacked by just 1 person stationed next to the car. They didn't even need to know just where the fob was, it only needed to be within range of the boosted signal, and within normal button-press range (e.g. in adjacent house or apartment). That meant the weak continual signal getting boosted was at the car side, not the fob side.
     
    #35 fuzzy1, Oct 6, 2019
    Last edited: Oct 6, 2019
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  16. 2012 Prius v wagon 3

    2012 Prius v wagon 3 Active Member

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    Well according to Schroedinger, it's both there and not there at the same time ... until someone finds it there or elsewhere.
     
  17. GFO

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    I like the stuck midway in an alternate time-space continuum theory best here as the explanation.
     
  18. Grit

    Grit Senior Member

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    How about placing thick foil over certain areas of car floor, and when car no longer goes into ready, fob must be in that area in under floor.
     
  19. The Electric Me

    The Electric Me Go Speed Go!

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    I think I like the idea of somebody placing foil all over the floor of their Prius.
    Then when people inevitably ask what they are doing?
    They can say " I'm testing to see if my Fob is in the vehicle OR whether it has fallen into an rip in the fabric of time and space. "

    Be sure to make yourself a cap at the same time.
     
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