Here's a decent rundown.
https://hackaday.com/2025/02/28/tech-in-plain-sight-shopping-cart-locks/
this post was submitted on 28 Apr 2025
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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.
Because the former location just virtue signal, the latter can't afford to lose the majority of customers.
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.
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
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.
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?
Am I not allowed to ponder it? I've never seen anyone doing it. The second some jackwagon was able to change the price on a gas station sign with a flipper it was hot news.
Turned out to be a neat rabbit hole.
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 wouldn’t* 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
I was paraphrasing, but fair enough.
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....
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.
Oh man I love the page view counter at the bottom.
I use this constantly by the way heh
Bluetooth speaker with a coil instead of a speaker?
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.
I thought about doing this the day before Thanksgiving or Christmas, imagine the shitshow
I'm honestly shocked this doesn't happen.
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.
Bubbles has joined the chat.
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.