It’s inconspicuous — an old service garage on an East Boston private way with pickup trucks outside and the roar of the airport behind it. The inside tells a different story: There’s a four-bedroom apartment in the back meant to serve as a “crash pad” for up to 20 flight attendants.

The City of Boston took control of the property and condemned the building on Wednesday after one resident reported a faulty smoke alarm to the fire department. The investigation and enforcement unit told GBH News the property owner didn’t have authorization to convert the commercial space into housing.

“It’s completely illegal,” said city inspector John Meaney, who was a responder to the call.

The space had four bedrooms with several bunkbeds and two bathrooms, along with a kitchen, according to photos shared with GBH News.

"This unit was constructed illegally, stored hazardous material, was missing smoke detectors and had no second means of egress," the department wrote on Twitter.

The city conducted interviews with at least one of the flight attendants, who said they’re paying $300 a month for a bed in the apartment. They were getting a good deal — a room at the nearby Embassy Suites by Hilton Boston is $200 to $300 a night.

The garage up front was being used as a warehouse. From the public bike path behind it, air conditioners can be seen in windows with wood covering glass that would allow visibility into the space.

In photos, there didn’t appear to be many possessions in the bedrooms.

“I’ve never seen anything like it before,” said Meaney, who has worked with inspectional services for 37 years. “I’ve seen rooming houses but not a crash pad.” The difference, he said, is that for flight attendants, they stay in a designated crash pad for a couple of days between layovers.

The property is owned by Solskinn Properties, and Aaron Daigneault is registered as its executive officer.

Inspectional Services said Daigneault and one flight attendant were present when they arrived on April 5, but he left without joining them on the inspection.

Daigneault told GBH News via email that when he bought the building, it was a warehouse space and one apartment, and he collected $3,600 a month from one tenant. He told NBC10 Boston that he rented the second floor of the building to a woman, who sublet the space, adding all the extra beds without his knowledge.

“We rent apartments to single or multiple occupancy tenant bases with a strict lease through an online property management platform. This unit was rented as a four bedroom apartment,” he told GBH News, adding that it’s “not a crash pad,” and the tenant on the lease agreed to move.

But on the fridge of the 37 Geneva Street space is a laminated poster, entitled “37 Geneva- Crashpad Rules.” Among those guidelines: Don’t give the door code to anyone, all “conduct and activity will be lawful” and spend 15-20 minutes in the bathroom — max.

Daigneault disputed the city’s claim that the space is dangerous, saying there’s “a second egress” or way to leave during a fire, through the warehouse, where tenants have “two doors to the outside.”

Inspectional services doesn’t agree.

“Worst case scenario, if you had everyone up there at one time, and there was a fire — it’d be a death trap,” said Meaney. The department said Daigneault can either go through the process to make the space legal and get it denied or approved, or dismantle it.

“I completely respect and am ready to work with all City of Boston officials moving forward to permit any and all use,” said Daigneault, who is a local real estate agent, and additionally owns Acorn Development, a construction company.

Neighbors didn’t seem too surprised by the bust. “I’ve noticed quite a bit of activity from people who seem to work at the airport, especially flight attendants, coming in and out of the building all day,” said a neighbor named Nate, who didn’t want his surname published for privacy reasons. Another neighbor told GBH News that she had seen flight attendants walking into the building since 2014.

Inspectional services is hearing from neighbors that the scheme has been going on for a decade.

“The apartment is registered annually with ISD Housing Rental registration division since 2016 as per requirements,” said Daigneault.

Inspectional Services said they’re looking into that claim, but doubled down that it’s an unlawful space.

“It’s an illegal two-bedroom apartment with 20 beds,”- said Lisa Timberlake, spokesperson for the department. She said it’s important for residents to report similar housing situations. “We cannot have people living in this type of dangerous environment,” she said.