Trader Joe’s has attracted a devoted fan-base by doing things a little differently than your typical grocery store chain. But shoppers may not even realize that the company has done away with this ubiquitous supermarket feature.

As Business Insider recently noted, Trader Joe’s doesn’t use an intercom system. So instead of hearing “clean up in aisle 4” blaring overhead, customers shop to a soundtrack of ringing bells.

The nautical bells, which are situated at each register, are used by employees to communicate with one another. According to the company’s website, “blustery PA systems” didn’t fit the brand, so it borrowed inspiration from the maritime traders of a bygone era and developed its own Morse-like code.

If you hear one ring, that means an additional register needs to be opened. Two rings means that either a cashier or a customer has a question at checkout, and three signals a manager. The code isn’t exactly a secret as it’s available for anyone to find online, but memorizing it will definitely give you bit of intel most patrons don’t have. It can also be used to plan your shopping strategy. If you hear four bells, for instance, that means the store is getting crowded, so you should forget about grabbing that second bottle of Two-Buck Chuck and hustle to the checkout line.

[h/t Business Insider]