Shopping carts are surprisingly expensive. Prices range up to about $300 for a cart, which may seem like a lot, but they have to be pretty rugged and are made to work for decades. Plastic carts are cheaper, but not by much.
And carts have a way of vanishing. We’ve seen estimates that cart theft costs hundreds of millions of dollars worldwide annually. To stem the tide, stores sometimes pay a reward to people to round up carts off the street and return them to the store — it’s cheaper than buying a new one. That led [Elmer Isaacks] to patent a solution to this problem in 1968.
The [Isaacks] system used lots of magnets. A cart leaving the store had a brake that would be armed by running over a magnet. Customers were expected to follow a path surrounded by magnets to prevent the brake from engaging. If you left the track, a rod passing through the wheel locked it.
A third magnet would disarm the brake when you entered the store again. This is clever, but it has several problems. First, you have to insert magnets all over the place. Second, if someone knows how the system works, a simple magnet will hold the brake off no matter what.
There are some low-tech ways to stop theft, too. For example, if the store has barriers too narrow for the carts to pass, customers can’t leave the store. That’s not very nice if you are trying to get a week’s worth of stuff to your car. You sometimes see poles on carts rising taller than the door, to prevent the cart from leaving the building, which, of course, has the same problem.
Some stores, particularly Aldi, require a small deposit to get a cart. You get the deposit back when you return the cart. This not only discourages theft but also cuts down on having to hire kids to round up carts in the parking lot. The problem is that the deposit is usually a low-denomination coin, so if you really want to steal a $200 shopping cart, losing a quarter is probably not much of a deterrent.
Higher Tech
Building on the [Isaacks] solution, more modern systems use a perimeter fence — usually a wire, but sometimes magnets — that causes the brake to engage if you roll the cart over it.
This drives the cost up and is expensive to install. Worse, if you only have one wheel lock, a smart customer could lift that wheel off the ground and bypass the virtual fence. That means you probably want two locking wheels, although that still doesn’t preclude a strong thief or two thieves from carrying the cart over the line. You can see a breakdown of what’s happening in the Science Channel video below.
Smart cart locks can also help solve “pushout,” an industry term for people filling a cart and walking out without paying. A properly equipped cart can determine if it exits the store without going through a checkout line. This is probably error-prone and not foolproof, but it might stop many pushouts.
Where’s the Hack?
Many common carts use 7.8 kHz signals on the sensing wire. Since that’s within the range of audio, you can actually hack them pretty easily.
A DEFCON presentation shows how you can use your phone to lock and unlock shopping carts. Not that we suggest you do that. As [Joseph Gabay] notes: “I never really wanted a shopping cart, but…I have the knowledge that if I wanted a shopping cart, I could have one.” His video below shows many of the internal details of some of the common shopping cart systems.
Who Knew?
You’d think a shopping cart was about the simplest thing you’d deal with all day. But, like many things these days, it conceals some very high-tech electronics. And it seems like there should be some better options. Locking wheels might be fine when you have someone actually stealing, but if you ever have a cart lock up while you are moving quickly, it isn’t pleasant.
If you become super interested in shopping carts, the National Museum of American History has a section of shopping carts. Why not? People get obsessed with strange things. If the modern system seems familiar, maybe you are thinking of invisible doggie fences. If you want to hack a cart, you probably want to buy your own to start with.
Featured image: “Large Capacity Shopping Cart” from the National Museum of American History collection.
“the store has barriers to narrow for the carts to pass” –> “too narrow for the carts to pass”
Thanks, and fixed.
I’ve never seen a store in the UK that prevents shopping trolleys reaching the car park.
The £1 coin slot does most of the work of preventing theft,. If someone really wants a shopping trolley, they can steal one, but I’d bet at least 80% of theft is kids messing around, and the £1 makes it cost something, which is too much (plus means you actually have to come prepared with a £1 coin to do it… less common these days!).
The next biggest group will be people who want to push their stuff home (and don’t have a car and aren’t using the bus…)
They’re determined, though given they’re probably low income, that £1 is more meaningful. But also as the trolley is heavy (or they’d just carry it home in bags) lifting it over the security wire is hard.
Adding to that, narrow exits on footpaths mean that they’ve got to push it out the car exit, which is risky and very noticeable on CCTV.
So my guess is that whilst trivial to defeat, those measures cut the vast majority of thefts?
We had a German exchange student who brought (as a gift) a keyring that held a fancy little Euro-sized disk – Instead of putting a Euro in the cart, you’d put this is an grab it when you’re done. But we don’t have anything like that in the United States. I still have the thing somewhere… I wonder if I’ll remember to bring it along when I get back across the pond.
Just 3D print them.
I have a double sided $1 and 25 cent.
So I don’t need to look for coins.
If you go as far as printing it, do it with the version you can wiggle out: to not let your keys hanging, proper hacker way.
It’s so tempting to build one of those signal generators into a wand so I can run around stores tapping shopping carts and cackling “spell of holding; roll 4 or less on d20 to escape”.
I don’t think anyone where I live ever actually wants a shopping cart – I expect there are two groups: Students who are drunk late at night take a shopping cart, ride around in it, and then throw it into the canal. Or people who live in walking distance of the store, who use the cart to bring their shopping home and then abandon the cart somewhere outside. Or throw it into the canal.
“Throw it in the canal” is the problem. Our neighborhood flooded after just a moderate rain. Water damage to many houses. The county investigated and ended up removing almost 200 carts from the canal. This was along a path thru the woods leading to a low-income neighborhood. They would push the cart with their groceries as far as the canal, but then couldn’t get it across the narrow foot bridge so they simply pushed it in the water.
A few years later it happened again. And a few years later, yet again. They county ended up installing a bridge that you could get a shopping cart across.
In California, it’s the homeless that take/ use shopping carts outside the store to move their stuff around town.
Have you suggested to them that they try not being homeless?
I’ve definitely been on the sad receiving end of a shopping cart wheel lock inexplicably lock up in the middle of the store. It’s like running into a steel bar right at waist height at full walking speed. Unfun, zero stars, do it recommend.
I remember the first time I saw one of these I was so fascinated I parked my car to try and test out the locking mechanism. It didn’t work, and I was pretty disappointed.
Fast forward about 10 years and my local supermarket installed them. I had the cart break activate while I was headed toward the door with the goods I’d purchased. I had to wait until someone could come unlock it. It had the strong feeling of legitimate users being hampered by DRM…
brake
Here in the Netherlands pretty much any store requires a coin. Often the stores even hand out dummy coins when asked, aka the german exchabge studebt story from above.
During covid most stores allowed for coinless use, by taping the slot or some such. Some stores (hornbach for example) kept them coinless, all others returned to the old ways.
This all probably for exactly the reason of theft. Damn kids and their ‘jokes’ … ot maybe its the returning thing? I have a metal dummy coin on my key chain that I can easily pull out after unlocking the cart …