Once upon a time, offices had walls inside them. They weren’t glass, like the conference rooms of 2019, but were made of drywall, and were usually painted a neutral color, like many of the walls you know and love. Over time, office walls gave way to cubicles. Now, for many office workers, the cubicles are also gone. There are only desks.

If you’re under 40, you might have never experienced the joy of walls at work. In the late 1990s, open offices started to catch on among influential employers—especially those in the booming tech industry. The pitch from designers was twofold: Physically separating employees wasted space (and therefore money), and keeping workers apart was bad for collaboration. Other companies emulated the early adopters. In 2017, a survey estimated that 68 percent of American offices had low or no separation between workers.

Now that open offices are the norm, their limitations have become clear. Research indicates that removing partitions is actually much worse for collaborative work and productivity than closed offices ever were. But something as expensive and logistically complicated as an office design is difficult to walk back, so, as Jeff Goldblum wisely intones in Jurassic Park, life finds a way. In offices where there are no walls, millions of workers have embraced a work-around to reclaim a little bit of privacy: wireless headphones.

Read: How to make your open office less annoying

The arrival of these now-ubiquitous devices has ushered in a new era of office etiquette—and created a whole new set of problems.

Unlike their tethered forebears, Bluetooth wireless headphones are convenient because they allow workers to forget they’re wearing a device and to leave their desk without yanking their laptop onto the floor. In open offices, people commonly wander around with their headphones on all day, into bathrooms and kitchens, sometimes listening to nothing at all in order to avoid the constant distraction of compulsory social interaction.

We have Apple to thank for wireless headphones’ proliferation. The tech giant launched its tiny white AirPods in late 2016 to accompany new iPhones that lacked a traditional headphone jack. Despite initial concern that having two plastic sticks poking out of your ears might look insurmountably lame, AirPods have avoided the demise of other wearable tech such as Google Glass by being immediately useful. Industry analysts estimate that tens of millions of pairs of AirPods have been sold already, accounting for as much as 85 percent of the wireless-headphone market. The earbuds even star in ultra-viral videos and TikTok memes as a jokey symbol of wealth among teens.

For Americans who have already joined the office workforce, AirPods serve a different purpose: tuning out your co-workers without looking excessively hostile. In that capacity, they’ve become indispensable to lots of people because the hard surfaces, high ceilings, and empty spaces common in open offices help sounds carry. There’s rarely any soft surfaces to dampen them. Jerrick Haddad, a 35-year-old social-media strategist in Brooklyn, won’t go to his open office without wireless headphones. “We moved from offices to an open plan two years ago, and wireless headphones are why I haven’t quit,” he says. “One day I forgot them, and I got up and walked straight to the Apple store to buy a pair of AirPods.”

The same is true for Antigua Samuelson, a 29-year-old Los Angeles resident who works for a medical-marijuana wholesaler. She watches Netflix or Hulu at her desk during slow periods, and without her AirPods, she’d have to find another way to fill significant amounts of idle time. “If I forget to bring them with me, I will go back home and get them,” she says.

According to Ethan Bernstein, a professor at Harvard Business School who studies organizational behavior, it makes sense that this subtle tactic for avoiding constant interaction has seeped into office environments. “People are very good at creating spaces for themselves, and these days you look at everybody and almost without exception they’re on their phones with headphones in their ears,” he says. In a 2018 study, Bernstein and his team found that open offices decrease face-to-face interaction among co-workers by as much as 70 percent, in stark contrast to the designers’ stated goal of collaborative teamwork.

The proliferation of small wireless headphones may exacerbate that effect. Since you don’t have to remove AirPods to wander around the office, it can be hard for your co-workers to tell if you’re listening to music or on a conference call, or if you’ve simply forgotten to take them out. For Samuelson, sometimes that’s the point. “Once in a while, I’ll pretend to have them on just so I can eavesdrop on what people are saying,” she admits. And for people who find music as distracting as they find their co-workers, putting on their quiet headphones can be as much of a visual signal as an attempt to dampen ambient noise.

It’s not a perfect system. David Grilli, a 33-year-old IT professional, uses his headphones to signal that he wants to be left alone, but the message doesn’t always translate. His co-workers “stand in your field of vision until you take notice and ask what they need, or they start talking immediately as if you’re not wearing headphones,” he says. Grilli’s co-workers might just need his attention at inopportune moments, but it could also be true that office workers are becoming so used to seeing one another in headphones that they barely register them.

For women, there can be an extra wrinkle: Wireless earbuds are often so small that they’re entirely invisible under long hair. Bernstein suggests that to send a clearer do-not-disturb signal to colleagues, people might consider larger, over-ear models.

Employers can do some things to help with the confusion, such as retrofitting a space with small, private phone booths to give employees somewhere to escape. That solves another headphone problem, too: Even when people can see your AirPods, they still don’t know what you’re doing with them. A person quietly sitting in on a conference call looks pretty similar to a person who’s focused on work while listening to soothing nature sounds, or to one who’s checking Facebook while listening to nothing at all. This ambiguity has prompted a whole new visual language meant to mime the difference to unsuspecting desk-mates. To perform its most common gesture, which indicates that you are on a call, you dramatically motion to your ears while making a face that communicates a sense of semi-smug capitulation: You, too, are currently being inconvenienced by your own importance.

Read: Zen and the art of cubicle living

“I do a lot of strategic hair tucking, gesturing at my ears, and phone pointing,” says Lisa Derus, a 31-year-old publicist who frequently uses her AirPods for calls both on her long commute from Connecticut to New York City and in her open-plan office. “I learned the hard way that the same ear-tapping motion I’d historically used to signal I’m on the phone is the exact same gesture that ends phone calls on my AirPods.”

According to the design psychologist Sally Augustin, all of this irritation has come about because open offices ignore some essential elements of human psychological development. “We get revved up just being around other people, so in a workplace you’ve always got that force energizing you,” she says. “When you’re doing intellectual work, you’ll do it better in an environment that’s generally less energizing.” Although headphones can help filter auditory interruptions, they can’t block visual ones, which Augustin says can be just as disruptive to performance and focus.

AirPods also can’t change the fact that you’re just sitting in the middle of an open room, which Augustin notes is stressful no matter what you’re doing. “When you can be approached from the rear, a little part of your brain is always vigilant,” she says. “It’s not about what you’re looking at on your screen or anything. It’s much more fundamental than that.”

The good news is that trends are already turning away from open offices in favor of designs that have a range of space types, including those that allow workers privacy and relief from constant stimulation. “This is how humans work,” Augustin explains. Evolutionarily, our open-plan stress response goes back to a time long before office politics. “We like to think we’ve come so far from our days on the savanna, but maybe not.”