Lock Your Keys In The Car On Purpose With Aluminum Foil

[TJ] is a surfer, and drives his car to get to the beach. But when he gets there he’s faced with a dilemma that most surfers have: either put his key in your baggies (shorts) or wetsuit and hope it doesn’t get lost during a wipeout, or stash it on the rear wheel of his car. Hiding the keyfob by the car isn’t an option because it can open the car doors just by being in proximity to the car. He didn’t want to risk losing it to the ocean either, so he built a waveguide of sorts for his key out of aluminum foil that lets him lock the key in the car without locking himself out.

Over a series of trials, [TJ] found out that his car, a 2017 Chevy Cruze, has a series of sensors in it which can determine the location of the keyfob based on triangulation. If it thinks the keyfob is outside of the car, it allows the door to be locked or unlocked with a button on the door handle. If the keyfob is inside the car, though, it prevents the car from locking via the door handles so you don’t accidentally lock yourself out. He found out that he could “focus” the signals of the specific sensors that make the car think the keyfob is outside by building an open Faraday cage.

The only problem now is that while the doors can be locked, they could also can be unlocked. To solve that problem he rigged up an ESP32 to a servo to open and close the opening in the Faraday cage. This still means there’s a hidden device used to activate the ESP32, but odds are that it’s a cheaper device to replace than a modern car key and improves security “through obscurity“. If you have any ideas for improving [TJ]’s build, though, leave them in the comments below. Surfers across the world from [TJ] to the author would be appreciative.

73 thoughts on “Lock Your Keys In The Car On Purpose With Aluminum Foil

  1. Maybe you could place a capacitive key pad on the side window. attach temporally it to the inside using suction cups. then you don’t need to take any device with you.

  2. Hide a sensor under a fender well, bumper or other hidden spot. Wave your hand it front of it and the servo moves. Make the sensor so you can move it from place to place, so no one can watch you once and know where it is. Something along those lines. Hell, put a switch behind one of the plastic body parts that give a little, then you just walk past it and push in the right area, and the servo, again, moves.

    1. Howabout two pads on the roof you have to put your hands on then speak to a microphone hidden in the B pillar door gaps “I am a meat popsicle” and it will verify your voice print and open.

        1. Maybe somebody thought of this first, there are alot of comments and I didn’t bother scanning through them all, you could just buy one of those magnetic key boxes. They are usually made of metal (steel) and would act as its own Faraday cage blocking the key fob from unlocking the doors. Just don’t be stupid about where you put it on the car.

  3. Firstly, I’d say he wants to try that in a wide open field to be sure it’s not environmental reflections allowing him to do it, i.e. the big wall of aluminum siding he’s standing right next to that we can’t see in the video or similar.

    Secondly. It does not look like a very complex operation to gain entrance to the car, which any criminally minded person may quickly pick up on having seen it once.

    Thirdly. Even if fancified (Or maybe even more so) the box on dash looks too “interesting” particularly if it’s got wires going to it. Junkies will think you stick your GPS in there, and despite GPSs only fetching maybe $5 at a pawn shop these days, that’s $5 closer to a fix so junkie will happily smash through $500 of glass for it.

    So suggestions..

    Firstly: TEST

    Secondly: Moar buttons… even 3 or 4 in a row, spaced one per finger, much harder to notice the “pin” sequence with only a small movement of each finger.

    Thirdly: Run the wires under the dash console and come up right under the box, which should be disguised as maybe the foam or cardboard box of a popular burger chain, or chicken chain, that looks like it’s just carelessly left on the dash.

    1. Oh for thirdly… don’t have to have the box permanently wired in place, which would be in the way of driving vision, or possibly airbags. (Check airbag locations before digging into dash) could use a regular 1/8″ jack socket in the dash with a mating plug on the box so you just plug it in on top.

      1. A button activates the door on the box to expose the key. So it’s not always in view. Was my first thought as well, because the article does not describe the setup very well, you have to follow the link to figure it out.

    1. This was my idea. Or make a copper version of those magnetic key stash boxes that you stick to the undercarriage somewhere.

      I’m glad my truck is crummy enough and I live in an area that’s old-fashioned enough to not need to worry about locking anything :) lost my truck keys a few years ago, so I’ve long since eliminated the keyed ignition. To get it moving you just flip a toggle switch under the dash and press a starter button with your foot. Never have to worry about losing my keys again and it’s never caused any other problems. I like living in low-sec land sometimes. It also helps that it’s a standard transmission with ruined synchro, so you’ve got to kind of double-clutch a lot of the time. That’s the real anti-theft device!

      Just once I’ve gotten in the truck after parking on the street and found somebody had rummaged through the glovebox, but I guess there wasn’t anything worth taking except a couple cigarettes. Didn’t even swipe the whole pack. Maybe there is honor among thieves, or at least among smokers. Anyway, I’ve definitely enjoyed those features when parking at the beach as well :)

    1. I agree with this, or somethnng as simple as building a shielded can and hiding that someplace under the car with the keys in it. Locking you keys in the car sounds like a good way to wind up having to ask some stranger if you can use their phone to call roadside asssitance to get you back in. The other thing to consider is just leaving your car unlocked. My friend in NYC decided that it was less expensive and easier to replace a cheap car stereo than have to file a claim to get new glass.

    2. It’s surprising how easily water can pump keys out of a pocket, it would have to be zipped. I once lost a set of keys (hire car and motel room) in the seal on a Florida beach, out of my trunks pocket.. Luckily the sea was calm, and clear, and I stayed calm, and found them on the sea bed!

    3. They sell the physical key blades for a few $. Glue it to a piece of plastic or something and take that with you when you surf.

      Bonus: You can lock the car with this too and not need to hack the system.

  4. Maybe a combo lock the mechanical key goes inside, like real estate agents use on front doors? A lot of cars have tow points or such underneath that the lock could clip to, and then the key is in a faraday cage with physical security. (Not much: even I can open one of those in a few minutes, but it beats trying to simply hide the key.) If there’s nowhere on the car you can clip a lock to, you can lock a chain around/through a wheel.

      1. A true hack would be to gut the zenith space command from an old TV and to take that remote with you. The remote was all mechanical (ultrasonic). Even funnier was they were notorious for going off when people jingled their keys. And it would excite the HAD people becasue the receiver was tube based. What could be cooler? Oh wait, an adruino made out of 12Ax7’s.. But shy of that, this would be pretty cool.

          1. The tubeduino would, but the nuclear reactor that it would take to power it might not… You might be able to mount in on a train and make a cool portabel POV display.

  5. My solution to this would be to put the key fob in a complete Faraday cage and take your phone with you. Since it’s a Chevy you can use the OnStar app to lock and unlock the doors with your phone.

      1. That’s a good reminder. When I upgraded my iPhone, I asked an Apple shop assistant the difference between my current phone and the new one. He dropped in that the new one had a higher waterproof rating.
        I stopped him – “you mean my existing phone is waterproof?” “Yes, sir”.
        Samsung’s high-profile waterproof phone ad had left me thinking that Samsung phone was the only waterproof one around. Turns out most are, they just don’t sing about it, as no one will replace under warranty for water damage if something does go wrong.

  6. Maybe I’m missing something… but how does needing to carry a phone or homebrew electronics project with you in the water seem like more of a solution than just carrying the waterproof RFID car key? This seems like an overly complicated and less reliable “solution” that doesnt solve the original problem of not wanting to take a key in the water. Sure, you no longer need to take your key with you, but now you have to take a bulky and fragile wifi-enabled electronic device with you? And at the expense of having to leave your key in your car so a smash&grab turns into your car being stolen?

    I must be missing something…

    1. If a hackaday writer was describing a ladder they’d say it was like two Es glued together that let you levitate up to high places …. and you’d be imagining a triplane when the original source said plain as day it was a portable set of stairs for easily climbing onto things.

  7. most wireless keys have a spare key so…
    open keyfob and remove battery, remove fob spare key.
    stash opened fob and fob battery in car.
    hide fob spare key somewhere else on car, magnetized to under body.
    use spare key to enter car, alarm will countdown/warn, wave the still battery-less fob near the “keyfob has a dead battery” sensor, usually on the steering column.

    tl;dr. disable the rfid, stash the manual key, go surfing.

  8. Could put the fob in a Faraday cage instead of removing the battery. The sensor in his vehicle is below the front cup holder. Copying the spare key might even make it work without disabling the RFID, unless the physical lock mechanism is blocked from locking rather than just disabling the door buttons. He can also use the Chevy app, or OnStar to lock and unlock the car if he brings his phone.

  9. Dear “Just take the phone” people…

    Active sports frequently involve tumbles that resemble being beaten with a baseball bat. Even your “bullet proof” otterbox isn’t going to do much when you take the only rock in miles to the hip when you’re being rolled in the surf like a ragdoll.

  10. Secret Knock.

    I had a similar problem with bike racing. Everyone left the key on top of a wheel.

    I found a hackaday article that used an arduino attached to a piezo sensor to listen for a coded knock and open the door on the correct code. I wired it into the switch attached to the driver’s side mechanical door lock. Sensor was taped to the inside of the sheet metal of the door. This unlocked the door and disabled the alarm. A different code would lock it and close the windows and sunroof. Might be tougher with a modern car. Mine was a 2000 VW.

    Piezoelectric secret knock controlling the faraday cage door would eliminate the need to carry anything.

  11. Instead of having to carry or hide a key fob some where to gain access a solution that uses existing hardware or discreetly placed sensors that are not obvious, like switches on a door handle or an trim piece that have to be pressed in a changeable pattern or number of times via a microcontroller more security could be had by having the system only accept a code at certain minutes after the hour synced to the vehicle clock visible from outside that way someone who saw him enter the code and tried it wouldn’t be able to get in as the code only works at 3,5,7,and 11 minutes for example.

  12. “Five long years, he wore this watch up his a22. Then he died of dysentery, he gave me the watch. I hid this uncomfortable hunk of metal up my a22 two years. Then, after seven years, I was sent home to my family. And now, little man, I give the watch to you.”

  13. I have been surfing for over 30 years and never seen a need for anything like this. I have never had a key come if the key loop in my boardshorts, but I have always had zipper or Velcro pockets too. I normally lock my keys & remote in an anti-static bag in the car and carry my valet key in the water, or a cheap generic dumb key if I have my wife’s car.

  14. I am normally in awe of the intelligence of most who post here on Hackaday. I myself, am normally silent as I am not worthy of such displays of intellect. Yet the responses to this query fill me with dread for the future of humanity.

    RFID, Bluetooth, faraday cages, etc.

    There’s already a much simpler solution to all of this. Go surfing with a friend, you put your car keys hidden under his wheel arches, he puts your keys under his wheels. So stuff the high tech solution, just get out on the water and surf.

    If anyone grabs the keys, they won’t work in the car you’re on, and it’s hard to find out which car they belong to. If you have hi-tech keys, then take the batteries out.

    If you’re surfing on your own, then we just hide our keys under a plant somewhere along the coastline. given a lack of plant/vehicle correlation databases, this security mechanism works quite well.

    I’m quite geeky yet profoundly let down by the lack of common sense shown in so many of the answers above. Surely hackaday people are up for finding simple, effective solutions. SO why all the tech stuff in the comments?

    1. Meh. Too much coordination effort — Shane was always late anyway. I just put my keys on my flip-flops on the beach. (Above the tide line!) Provides perfect security at the bottom of a 150 foot cliff at 6:30 a.m. Stingrays and dolphins don’t steal cars.

      Still, you can drive away with half of San Diego if you just look on top of the rear driver’s side wheel. :)

      But that’s missing the point: this is a servo-activated aluminum-foil-and-cardboard Faraday cage.

    2. It’s not hard to figure out which car it goes to. You just press the panic button. If it has proximity sensor, it is most likely the remote too. If you know what make the vehicle is, you would only have to check a small percentage to find it if there’s no remote.

  15. Almost all cars have an ordinary key lock for when it is locked and the battery dies. You can get such an ordinary key (without the starter disable transponder) from most hardware stores. Also after an experiment, I found a key that just had a hole at the end of the shaft which was inserted to my (broken) remote fob, so it was even smaller.

    In my case it is a Ford F250. I learned the hard way that you always want THREE starter security transponder keys, because if you lose one, you can authorize a third with the other two. I think the max is 4 keys and 4 fobs. You can place a transponder only “key” (uncut or with the key part removed) just below the ignition keyway and the plain key will work.

    So technically there are three separate pieces, the remote lock/unlock (plus alarm, and if the bit is set, remote start), the security transponder, and the physical cut key. You need the key to enter the car, but also the security transponder to start it. There are some other subtleties (remoted starting may count as an authorized key).

  16. I faced a similar problem a few years ago when I broken the locking cylinder while trying to open my Accord with the key. The cylinder just kept spinning so I ended up breaking the rear quarter window to get in. The solution I came up with was to attach two small cables to the inside of the side-mirror to the locking mechanism within the door. I push the mirror forward and it locks the door, pull the mirror back and the lock opens up. Maybe it’s not the best option but its one that works and nobody AFAIK has ever really figured out what I’m doing when I push or pull the mirror.. you could get away with just one cable for opening the lock.

  17. Go old school.. put a “trigger” on the outside that’s wired to one door. An never be worried about being locked out.
    If locking keys in car was a sport, wife would be M.V.P .

  18. Damn, I can not believe I did not thing of this sooner, but what about car surfing? Just take your car in with you. Not sure if you would use 1 big assed board or 4 smaller boards.. But how cool would that be? LIke be out on the ocean with tunes and AC, a cup holder and all…

  19. I miss my model year 2000 Ford. It had a 5 button keypad on it to unlock the drivers door. Parking was limited to 2 cars for our 4 bedroom college apartment so I’d stash my car nearby in town with a spare key hidden inside. Whenever I needed my car but didn’t want to walk home to get my car keys or needed to loan it to a friend, it was easy to just type in the code and drive off.

  20. Wrap the key around aluminum foil, place it in one of those magnetic key boxes and stick underside your car. Or …. most keyfobs have a physical key that you can detach from the fob, put key in cage and lock unlock the doors with the physical key, place the key on a necklace, strap … or same, put it in a magnetic keybox and stick it underneath your car.

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