Secrets of Electronic Shelf Labels

by Trailblazer  (trailblazer@usa.com)

While the supermarket experience is probably taken for granted by most of us, some will nevertheless notice that these places are technologically evolving.  Computer-based cash registers, laser quality receipts, and commercials running on flat-screen monitors are all commonplace in today's supermarkets.

Remember those clunky guns that spit sticky price tags, allowing even the slowest stockboy to price a case of canned soup in seconds?  Well, they've disappeared, too.  In most of today's supermarkets, you'll see a laser-printed label placed on the edge of the shelf.  Some supermarkets have gone a step further and introduced Electronic Shelf Labels (ESLs).  Through some social engineering during some late night shopping, I've learned a little about these things and would like to share this information.  Hopefully you'll find this technology as fascinating as I do.

These ESLs are simply small plastic panels with an LCD display, prominently fixed to display a product's price on the edge of the store shelf.  There are several companies that manufacture these products, but in my area's supermarkets there are two chief vendors: Telepanel Systems and Electronic Retailing Systems International.

  

Their price tags come in various shapes and sizes, sometimes with one LCD display and sometimes two.  In my local supermarket for instance, smaller items like spices and condiments have small displays; larger products like paper towels have larger tags.  Some even have hidden buttons that display additional information (product UPC codes in my limited experimentation) when pressed.

They're pretty rugged and if you've ever worked in a supermarket you'll know why.  These things need to withstand runaway shopping carts and bored children's busy hands.  I would guess they're also water-resistant for obvious reasons (or should I say raspberry jam-resistant)!

I've tried removing one of these tags from the shelf and it was tough.  The shelf edges were slotted to house the tag snugly.  Once I did remove it, I noticed the tag was powered by a wafer-type watch battery in the back.  I removed the battery, awaiting the obvious effect of the LCD display going blank.  I replaced the battery however, and the original price returned.  How?

The electronic price tag system is quite sophisticated.  Imagine the supermarket as a giant LAN, with each price tag being a node in that network.  Each tag communicates with a server somewhere in the back office.  This server receives a feed from a database running on the supermarket chain's main server, presumably located at its headquarters.

So price changes can be automated right down to the shelf.  For example, a supermarket bigwig at the headquarters decides the price of Jell-O needs to go up.  He makes that change in the database, and that change is pushed to each store's back office server which then sends that update to the label.  Voilà, the price has changed on the shelf, no price gun required.

That back office server is obviously part of the Point of Sale (POS) system, so you know you'll be paying that new price as the clerk is ringing you up for your Jell-O.

The means of communication between the price tag and the back office server is even more remarkable.  In my supermarket (an Electronic Retailing Systems customer) this communication is wireless - the labels communicate with their server via RF!  Cellular transmitters are mounted on the ceiling and transmit via a 2.4 GHz spread-spectrum frequency.  Price changes are distributed in this way.  When the label receives the message, the display is updated, showing the new price.

Though I'm not sure how, RF communication occurring between each label and the server is two-way, and it resembles a TCP connection.  Each label has a unique hex address (it's printed on the side), and it's constantly "listening" for messages containing its address from the server.

So when the server has a price update for a product, it transmits the price information as well as the address of the label for which that update is intended.  The label receives this data, then sends an acknowledgment message upon receipt.  If the server does not receive this message, it sends the price update again until the label replies.  I'm assuming the RF occurring is very low power - I counted three or four ceiling transmitters per 50 foot aisle.  I would also reckon the FCC would complain if we were looking at anything more than a fraction of a watt.

Experimentation with the electronic shelf tag systems is wide open.  If you own a scanner (see Sam Morse's article "An Introduction to Radio Scanning" in 17:4), bring it along the next time you go shopping and see what you can pick up.  Perhaps this communication can be disseminated for a better understanding of the whole process.

If you happen to wind up with one of these labels in your possession, take it apart and see what's inside.  Or better yet, try feeding your own signal to the label.  Those LCD readouts are alphanumeric, so you're not limited to displaying prices.  There is still the question of how the label displayed the data even after the battery was removed and replaced.  Are those transmitters constantly transmitting price information, or does the tag have a storage capability?  If there is storage, what other information can be found on an ESL?

If you happen to work for the supermarket and have access to that back office server, well, you've got an entire network of shelf labels to explore.  Just remember that changing the price of your favorite frozen pizza to a nickel is not something I recommend.

Supermarkets make only a percent or two profit for each transaction.  That such businesses would invest in such elaborate pricing systems poses many questions.  For example, how often are prices changed, to what degree, and when?  Who is benefiting from electronic shelf labels - customers or the supermarket corporations?

If you're a conspiracy theorist like me, then the answers are obvious.