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Control shopping cart wheels with your phone (2021)
140 mystraline 29 8/22/2025, 12:59:04 AM begaydocrime.com ↗
Original DEF CON 29 (2021) talk: https://www.youtube.com/watch?v=fBICDODmCPI
Losing a cart is expensive, but it doesn't seem to happen at the scale that would make a full blown locking wheel solution cost effective.
My favorite part of the system in larger stores is that to handle people not carrying cash (Sweden is pretty long-gone in this regard), you can usually go inside the store to get a free plastic token that fits the reader.
That always made me chuckle, since the entire point of the system is that you're supposed to be incentivized to return the cart to get your money back, so by replacing your money with a free plastic token that they hand out from a basket, they did .. something to the overall system design.
Still fun as an example of how the customer's overall experience is more important than the point of an entire security system, I think.
It was completely counterproductive, too. The edge of the zone was about 50% of the way home. Out of spite, we'd push the cart up to the edge, and leave it stranded there, carrying everything the last 200m ourselves.
Not proud of that in retrospect; it goes to show that you can't stop assholes with technology.
It's more also common in places where people walk, since it can be hard to bring groceries home on public transport.
So yes, very localized.
The shop near me doesn't have locking wheels (they used to, but stopped), instead they have a guy in a pickup that drives around occasionally, searching for carts.
Reminds me of the LoLRa project from cnlohr that transmits LoRa without a radio transceiver.
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> Since 7.8 kHz is in the audio range
What is "the audio range" in the context of radio frequencies?
The range of human hearing is about 20 to 20000 Hz. As a by-product of producing physical vibrations at those frequencies (i.e. producing sound) via an electromagnetic coil, a speaker will produce an EMF with the same frequencies.
1. The phone's speaker generates a small amount of EM intereference at the audio frequency it's playing at 2. The sound waves hitting the locking electronics cause them to vibrate at that frequency and pick up random noise from the environment as a signal.
Either way, by using a frequency between 20Hz and 20kHz, everyone has some kind of "transmitter" that can generate mostly arbitrary waveforms.
I hope someone attaches Bluetooth speakers to their shoes and locks every cart in target, so they have to remove the system.
https://hackaday.com/2016/03/04/social-engineering-your-way-...
Edit: looks like an Ardunio can do this with PWM too
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Friends did this college in like 2005. Cambridge area, Shaws Market I think. I imagine the hardware setup was a bit different. All the details are hazy but I recall their lock transmission signal had a huge range and locked all carts in a wide area.
Based on what I recall, I believe there was one on the southeastern end of Green Street, a bit between Central and Kendall Square, barely northwest of MIT's primary campus area on the corner Massachusetts Ave and Vassar Street. That location has apparently closed in recent years.
https://www.instructables.com/EMP-shopping-cart-locker/
It might been the same text that somebody copy/pasted there, sounds vaguely familiar.
Shouldn't be difficult to find carts left near or beyond the edge of the parking lot.
I find the locking wheels annoying, because they're so often defective and make it a noisy struggle to get your cart through the store. But years ago I also had a neighbor in my apartment complex who would walk home with a cart every week, and would just leave (a dozen of) them there... she couldn't be bothered to push the empty carts back to the store, not even once. I'd think a $1 deposit/return system for carts would work better, and give the homeless in the area some gainful employment.