Should a key-fob be stored a metal coffee can?

I’m having difficulty understanding this key fob security issue. I can see how a thief could intercept the fob’s radio signal with speciality equipment when you press the door-open or engine-start button, and then use that signal to open your car’s door and drive the car away. But I don’t see how storing the fob in a metal can when it isn’t being used would be of any help. Anybody here have an explanation?

With some cars, you don’t press a button on the fob to unlock the car; you just walk up to the car. The fob is clearly transmitting all of the time (although intermittently, I’m sure).

As for the metal can, look up a Faraday shield if you’ve never heard of that, although you’d probably need a metal lid to complete the enclosure.

I’ve said it before…but I sure miss plain ol’ metal keys.


Thanks for the explanation … hmmm … seems like the obvious partial-solution is to revert to fob designs that only transmit signals when the the owner presses a key. Receiverless fobs. As for the folks who grab the transmitted signal then use it to steal the car, it seems like the same method garage door openers use would work; i.e. a rolling code that changes each time the button is pressed.


The other “solution” is to keep your key fobs in a Faraday Box when they are not being used. These “boxes” are really not expensive, and that measure resolves several potential issues at a low cost.

You could just make a Faraday cage out of aluminum foil. You could also use a sardine or tuna can after it’s opened and seal the top with aluminum foil. Those metal cans that mints come in would be good too.

Just tried an experiment, key fob maybe 20 feet from the car in my coat pocket. Tried to start the 2017 rav 4, key not detected. Still can lock the doors with fob in coat pocket. Now the battery in the fob went dead one time, don’t recall if the doors were locked, but had to hold the fob near some point as directed to start the car, and it started. If you are that worried pull the battery from the fob if you can still start your car without a battery in the fob.

I was moving the 2020 Honda and the 2019 Toyota around in my driveway and wife was out there too. I had both fobs in my pockets and I asked the wife to move the Honda and when she sat down in the car without the fob, the car started “screaming” at her with its warning sound. She jumped out and told me to do it, I told her that proves she’ll never “steal” the Honda… L :smile: L . . .

When I bought my last new car in 2018 I searched for one with an old fashioned metal key, a big plus in my book. There weren’t many available but I found one and bought it.

My 2020 Honda and 2019 Toyota both came with a metal key. The key is an insert in the fob. Each vehicle comes with one mechanical lock on the driver’s side door, none on the passenger’s door, or on the hatch… Some members have written in that when they needed to use the mechanical lock, it was frozen/rusted up from none use… A point to consider to ensure you periodically check that the mechanical lock still works and make sure you know where to place the fob to start the vehicle in the event the battery dies. Most vehicles need the driver to touch the Start Button with the fob, one older vehicle needed the fob to be placed in the cup holder in the console. Do you know where your “special” spot is? As a test, I have removed the battery from the fob and then tested that I could get in the locked vehicle and start it with a dead fob battery…

You must enjoy trying to dig out a key when one hand is holding an umbrella and the other hand is holding grocery bags. I don’t.

Yeah, that’d work … lol … but I expect most car owners would say something less intrusive but equally secure would be better. I’m surprised the fob is designed to transmit all the time, just in case the car is nearby and listening. Seems like that would run down the fob’s small battery. The alternative is the fob is always in listening mode, doesn’t require much fob battery power for that, and the car is transmitting all the time. The car has the much bigger battery. Whether fob is transmitting or listening, the security problem presumably remains though.

A little planning can prevent this.

Could they use the same technology as RFID tags?

It doesn’t work because they are unlocking the door and starting the car while the remote link is active and the other thief is behind the person in line at the store intercepting the radio signal from their key fob.

They’re doing the same thing with the new in the USA smart card credit cards. While the card is in the machine, another transaction at some distant location is taking place. The smart card contains a private key or similar that is never revealed outside of the chip, so it can’t be copied and used later.

They are solving this car key fob problem using time of fight timing. The response must be received from the key fob within so many nanoseconds or it knows that the key fob is actually farther away than the radio receivers in the car detect.

They key probably has passive RFID is a backup.

They range is too short. RFID is limited to a couple of feet range. The transmitter has to generate a powerful pulse to power the RFID chip enough that it can send something back.

I still have a key. But my wife’s 07 Lexus is keyless. And she LOVES it. She likes the fact of not having to fumble through her purse for the key. The car is 17 years old and the only issue is we have to replace the fob batteries every 5 years or so. Doesn’t have to pull fob out the unlock the door. When she touches the drivers door it unlocks that door ONLY. She then has to manually unlock the other doors - of if she touches the handle of any other door - it’ll unlock all the doors.

A few days ago, I decided to browse through the “driver customization” details on my Lexus, and I discovered that I could change the door unlock function so that it unlocks all of the doors when I touch the door handle. You might want to check to see if this can also be done on her car.

One of the features that I really like on rainy days is the “kick open” feature that allows me to unlock the rear hatch when my arms are full, by simply passing my foot underneath the bumper. IIRC, your wife’s Lexus is a sedan, but I don’t know if this works on the trunk lid of sedans the same way that it works on the rear hatch of SUVs.

Actually she likes that. It gives her a sense of security knowing that someone she doesn’t want to get in through one of the other doors. I basically have that on my fob for my Highlander. Press the unlock button once and it unlocks driver door. Press it twice and it unlocks all the doors.

A key fob contains a short-range radio transmitter/radio frequency identification (RFID) chip and antenna. It uses radio frequencies to send a distinct coded signal to the receiver unit in the vehicle. This receiver also contains an RFID tag, which contains the stored information that identifies the individual fob

Key fobs typically do not transmit all the time. Instead, they are designed to transmit a signal when a button is pressed or when they are in close proximity to a vehicle or other system that they are programmed to interact with. This helps to conserve battery life and prevent unnecessary transmission of signals.

When the vehicle is triggered, either by pulling the handle or touching the handle, an LF signal is transmitted from the antennas to the key. The key becomes activated if it is sufficiently close and it transmits its ID back to the vehicle via RF to a receiver located in the vehicle.

I performed and experiment this evening, with the fob in a one-pound steel coffee can, I held the can in my hand and then tried to open the locked doors on my 2020 Honda and the 2019 Toyota. I could not get in the Honda, but the Toyota still let me in (my baby knows me…)

I then took a sheet of aluminum foil and folded it in half and place each fob in it one at a time and with the foil only folded over the fob, not wrapped in it, and with me holding the foil, neither car responded to me trying to open (unlock) the door. I opened the foil and both cars unlocked as normal.

By storing your car keys, fob or card in an aluminum tin (even grandma’s old biscuit tins), or a special signal blocking box, the signal between the car and key will probably be blocked. This means thieves can’t intercept it and clone a new fob to steal your vehicle. If you’re out and about, then a Faraday pouch is your best friend.

Or put your fob under your aluminum foil hat… L :smile: L


Thanks for the expanded explanation. But I still don’t understand how storing the fob in a faraday cage would help. You mention above the fob generally doesn’t transmit unless it is near the car. The owner still has to open the door and drive the car so must remove the fob from its protection then, at which point it is apparently vulnerable to thieves. It seems like all the thieves need to do is do their data stealing at public parking lots.

Car thieves can steal a car using what is called a Relay Attack. As I wrote, when a fob’ed vehicle is unlocked either by pulling the handle or touching the handle, the vehicle transmits out a really weak LF signal (sort of a “Hello” message) to the fob. If the fob is sufficiently close, this activates the fob and becomes activated it transmits its ID (“Yes it is I… Open sesame…”) back to the vehicle via RF to a receiver located in the vehicle.

The thieves use special piece of electronic equipment that is a powerful receiver and transmitter. They activate your door and the vehicle sends out it “Hello” but since it is very weak, the signal is retransmitted, but much more powerfully. The fob is now able to receive this, even in your home, far away. The fob then responds with its ID and that signal is picked up by the receiver, since it is so much more sensitive and sends it to the vehicle. The thieves can also program a new fob using this equipment.

So, back to your statement, “But I still don’t understand how storing the fob in a faraday cage would help.”

The faraday cage or even the aluminum foil blocked the signal so the fob did not hear the Hello message and if it somehow does receive that message, its very weak reply is too weak to penetrate the faraday cage or the aluminum foil…