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. A basic metal cart can be had for about $100 to $150, although shipping might drive that up, too.
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 to 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.