ingemarFeb 23
Mark Dominus

“Most electronic shopping cart wheels listen for a 7.8 kHz signal from an underground wire to know when to lock and unlock. A management remote can send a different signal at 7.8 kHz to the wheel to unlock it. Since 7.8 kHz is in the audio range, you can use the parasitic EMF from your phone's speaker to ‘transmit’ a similar code by playing a crafted audio file.”

This sounds improbable but I needed to use it just now and it worked both times.

https://www.begaydocrime.com/

Hack this Shopping Cart

Feb 21 at 6:29pmWeb
Show threadAidanFeb 21
@mjd phreaking cart!
Show threadboreqFeb 21
@mjd what shopping carts have lockable wheels these days? that is insane
Show threadI Thought I Saw A 2 Feb 21
@boreq @mjd lots of grocery store carts have a warning that the wheels will lock if you take them off the property to discourage people from stealing them. I thought it was just BS but I see I was wrong
To be fair metal grocery store carts are actually pretty expensive
Show threadboreqFeb 22

@ithoughtisawa2 @mjd

>lots of grocery store carts have a warning that the wheels will lock i

I've never seen this in my entire life, and no I don't live in a high trust society

Show threadThomas PhinneyFeb 21

@mjd As somebody living in the USA, I am very curious as to whether this is a DMCA violation or not... 😂

OK, I am MOSTLY joking, as I don’t see it.

But only mostly. sigh.

Show threadI Thought I Saw A 2 Feb 21
@mjd amazing. I always thought those warnings about the carts locking were just scare tactics. I have to try this next time I go shopping
Show threadJos DingjanFeb 22

@mjd @fanf I’ve had this tab open in my browser for a while now…

(And yes, I’ve tested it at our local supermarket - it works!)

Show threadMartin SchobertFeb 22
@mjd It reminds me of @henryk who used an ipod and a coil for signal replay of an LF transponder to open a door at a local university.
Show threadHenryk PlötzFeb 22
@nitram2342 @mjd Haha, I thought of that too. IIRC back then it was a ~2kbit/s data signal with Manchester modulation -> 4kHz edge to edge, leading to a Nyquist frequency of ~8kHz, deep in the audio range. I put the wav file on my iPod, hooked up the tuned coil, hit play, and the door opened before I even realized that it was working.
Show threadKevin Karhan Feb 23
@mjd There are free apps on #Android that can literally generate any frequency 10Hz - 20.000Hz and spit it out.
Show threadLisPiFeb 24
@mjd I'm vaguely surprised they're using audible audio for this.
Show threadDNA scheduleFeb 24
@lispi314 to be clear, the shopping cart is not using audio, they're using an electric signal that's in the audio range in terms of frequency, so an electric speaker playing at that frequency will also create a weak electromagnetic signal at a frequency that can be detected by the shopping cart circuit
Show threadLisPiFeb 24
@ryanprior Ah I see.

Huh. Neat.