Could I make a little gun and just walk around through the parking lot and aisles of the supermarket and freeze all the carts in place?
Here’s a decent rundown.
https://hackaday.com/2025/02/28/tech-in-plain-sight-shopping-cart-locks/
Yeah, I just watched a youtuber take apart a modern one. Found the maker and the manual for the system. Then watched some more people taking the system apart (including the one you linked)
Neat stuff:
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Looks like it’s <9 Khz signals (7.2khz in the one I looked up), at that frequency, you can do a replay attack using your phones speaker from 0 distance.
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the electronics in the wheels are potted, including the battery so they’re disposable at EOL.
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Apparently, the unlock signal is just an inverted lock signal. Easily detectable.
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Their system has the ability to lock/unlock all carts, only the carts left in the parking lot overnight.
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One of the features available is for them to identify and freeze a particular cart if it doesn’t go through a checkout.
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What’s interesting about these carts is that they only ever seem to be deployed at stores that I wouldn’t think were prone to cart theft, to begin with. They’re always in the nicer neighborhoods at the overpriced stores that nobody should be shopping at in the first place.
Meanwhile, every cart at the stores in the worse neighborhoods look like they’ve been used as target practice for an M1 Abrams tank, have no locks, and can be found scattered on random street corners for a 3 mile radius from the store.
Retailers in wealthier areas have larger budgets, higher profit margins, and more attention by the executives. The favorite managers get assigned to the better stores and regions because obviously it involves better bonuses and better quality of life. They then invest in bullshit security upgrades because they can, and the C-suite believes they work because, well, the managers saying they work were already the favorites.
Retailers in lower income neighborhoods literally can’t afford long-term investments - corporate runs them on razor-thin margins, assigns them the worst managers by default and doesn’t trust those managers, and underpays their staff such that they’re constantly dealing with turnover.
Even if they found the temporary budget to install the security measures, they would still need a permanent budget to maintain them, and it still wouldn’t be worth it because:
- if $X worth of shopping carts walk out the door, and you add $Y worth of security measures… now $X+$Y are walking out the door.
- if shopping carts are constantly locking up and malfunctioning due to underfunded maintenance, $Z worth of shopping carts are now sitting in the store doing nothing, which in the corporate world is almost as bad as that money walking out the door.
One of the proposed features is locking the cart if someone is about to walk out without paying.
The cost of the RF locking wheels isn’t far off the price of a replacement cart. (Not to mention the investment in digging up the entire outline of the lot burying the line.
Because the former location just virtue signal, the latter can’t afford to lose the majority of customers.
That was surprisingly interesting.
The hacker who did the Def Con talk linked in the Hackaday article also did another one, they are both very interesting
I want to answer your question, but
Could I make a little gun and just walk around through the parking lot and aisles of the supermarket and freeze all the carts in place?
Means I won’t do so. Why would you do that to people?
Didn’t say I would, the thought just occurred to me that there’s nothing stopping people from doing it save a little tribal technical knowledge.
I’ve never seen it happen, so it led me to wonder if it was possible.
Why would you do that to people?
Some people just want to see the world burn. Better something mildly inconvenient like this than, say, voting fascists into power for the lulz, I guess.
I vote for neither.
Your shopping cart will be the first against the wall when the revolution comes
<3
Because it’s funny.
I’m guessing it’s similar technology to invisible dog fences with an underground boundary wire with a signal that could easily be spoofed.
There are valid applications for it. It could be used to slow shop lifters if they are trying to use a cart to get to a vehicle in the parking lot. It could also be used to help close specific aisles or portions of the store where customers should not be.
This guy does not seem like he’s interested in ‘valid applications’, he’s interested in being a dick.
I would jump straight to “being a dick,” I have had many of these thoughts that I would never actually do in real life, but I want to know if it’s possible so I can shit on dumb technology hahaha
Yeah but you’re not posting ‘Hey, how do I do X?’ followed by an example of what you intend to do with X that involves you being a dick, either.
Hey, how do I do X
I didn’t ask. I’ve been doing electronics for decades, I own enough equipment to listen to the signals and create them if they work like I suspect they do. It’s a shower thought, I have no intention of doing it, well now that we’re all spicy here about it, I kinda want to try as a proof of concept.
I’ve never seen it done, was just pondering
Yes, there could be valid usecases to stop a cart, but the manufacturer of the carts should (and possibly already does) implement that and instruct the store on its usage/requirements.
Shopping cart wheels here only freeze for one reason: crappy bearrings that get jammed up when people run through pools of spilled grape juice and maple syrup.
They always make that one sound
Oh wow yeah. Like nails on a chalkboard!
Re re re re…
I thought about doing this the day before Thanksgiving or Christmas, imagine the shitshow
I’m honestly shocked this doesn’t happen.
Im not sure exactly how the system works, but if I were designing one, there would be 3 approaches I can think of.
The first is to equip the lock with a GPS system and dictate that it locks if it’s not within range of a particular location. This one would be the most expensive to implement, but should come with minimal opportunity for messing with it.
Next down the list is each lock is equipped with a radio to connect to a wifi or sub-GHz broadcaster, and as soon as it misses enough heartbeats to a central control point, it locks the wheels. This could be disrupted by jamming the signal, but jammers of this type are highly illegal, and easily trackable.
Last is the cheapest option, which is to include an RFID module tied to the lock and a system to broadcast a signal at the perimeter. If a cart comes within range for a long enough period then the RFID tag is activated and the wheels lock.
I suspect it’s probably a sub-GHz radio situation, with the broadcast power tuned to be within a few hundred meters of the store. If you had some kind of SDR you could probably pinpoint the signal they use and repeat it, letting you wheel a cart outside the zone, but as soon as you stop the signal the wheels will lock.
It looks like they’re SubG. The lock signal broadcasts on the buried line, and at least in the one manual I found, they can also lock all, lock all in a lot, and optionally lock singles via serial number (there’s an inventory system). There’s a directional handheld device that can be used within a couple of feet of an affected cart.
I always assumed it was a powerful magnet that was buried in the parking lot. The magnet triggers the lock. That seems the cheapest, lowest cost way. They have locking carts for over 30 years so it is unlikely to be a new technology.
It sounds like something you could accomplish with a device like the Flipper Zero.
Maybe, it’s actually pretty limited compared to a real SDR.
That would be hilarious!
You could probably do it with a Flipper, maybe? Those carts work on radio signals around here and I know you can use a Flipper to, like, change someone else’s TV channel or open their garage. You might even be able to keep it unlocked even after crossing the barriers.
I wonder the same thing. What I wonder even more, though, is why you think inconveniencing others is acceptable or funny?
acceptable or funny?
didn’t say acceptable or funny
I just wondered it.
This might actually be a good opportunity for an AI answer:
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First, understand the basic principle you’re working with:
Shopping cart wheel locks respond to a specific RF (radio frequency) signal (typically around 7.8 kHz to 10 kHz for many systems, but it varies by brand).
In normal operation, the boundary wire emits this signal constantly.
The unlocking posts emit a different coded signal to reset the wheel.
So to design a portable device that could lock and unlock wheels manually anywhere, you would need:
- Identify the Signals
You must figure out the exact frequencies and modulation patterns used by the cart system.
Different companies (like Gatekeeper Systems, Carttronics, etc.) use slightly different RF signatures.
Usually lock signal = basic broadcast (constant tone) Unlock signal = special modulated unlock code or sequence.
This might require:
A spectrum analyzer
Or reverse-engineering an existing unlock station.
- Design the Portable Emitter
The portable device needs:
A programmable low-frequency RF transmitter (around 8–10 kHz range, low power)
A microcontroller (Arduino, ESP32, etc.) to generate the right modulation if the signal is coded
An amplifier to make the signal strong enough to reach the cart wheels (they usually detect it within 3–10 feet)
Optionally:
Two modes: a “lock” mode (sending the boundary signal) and an “unlock” mode (sending the unlock code).
- Basic Hardware Components
Low-frequency oscillator (to generate 7.8–10 kHz wave)
Microcontroller (to handle switching, coding)
Coil antenna (for strong near-field transmission — like a small induction coil)
Amplifier circuit (boost the signal so carts sense it a few meters away)
Battery pack (portable, rechargeable — say 12V lithium-ion)
Mode selector switch (Lock / Unlock)
- Software
Simple microcontroller code to:
Emit plain carrier signal = Lock mode
Emit modulated code = Unlock mode
Example (pseudo-Arduino code):
if (mode == LOCK) { generateContinuousTone(8kHz); } else if (mode == UNLOCK) { generateUnlockCode(); }
- Important Challenges
Matching signal format exactly: If the unlock signal is digitally modulated (like FSK or ASK), you must match the timing perfectly.
Power levels: Too much power could fry circuits or interfere with nearby electronics. Keeping it safe is key.
Legal considerations: Broadcasting radio signals, even low-power ones, can be restricted depending on the country.
Simple Concept Sketch:
[Portable RF Cart Lock/Unlock Device]
Size: About a large walkie-talkie
Two buttons: Lock / Unlock
Coil antenna: About 3–6 inches
Range: 1–3 meters effective
Display: Small LED indicators (Locking / Unlocking / Signal OK)
In short: You’re essentially building a portable invisible “fence” generator with two channels: a “keep away” signal (lock) and a “come back” signal (unlock).
