Parents are reportedly sneaking $250 monitors into their kids' schools to test air quality. One company says sales have doubled.

• Parents are smuggling $100 air-quality monitors into school with their kids, NYT reports.
• During back-to-school season, sales for one popular monitor doubled.

On top of masks and hand sanitizer, some parents are employing a new tactic to keep their kids safe during a pandemic-era back-to-school season: air-quality monitors.

Parents are arming their children with air-quality monitors hidden in their backpacks and pockets to gather data on CO2 levels in the school building, which can indicate whether a space is well-ventilated and reduce the child's chance of catching COVID-19, The New York Times reported.

Aranet, a company that makes a popular CO2 monitor, told the Times that sales had doubled since the start of the school year. The company didn't immediately respond to Insider's request for comment. The company's home sensor costs $250.

Good ventilation can be critical in preventing the spread of COVID-19 in a classroom, even if all students are masked. If classroom air isn't well-circulated, the virus can accumulate in the air and put other students at increased risk of contracting the disease if one of their classmates is infected.

Schools have struggled with poor indoor air quality for years prior to COVID-19 and bad air quality from sources like mold and mildew has been linked to lowered test scores and learning. But during the pandemic, air quality in schools has become even more critical.

"The biggest risk comes from poorly ventilated, crowded environments where people spend a lot of time. Unfortunately, that kind of perfectly describes a lot of schools," Jeffrey Siegel, a professor of civil engineering at the University of Toronto, told Insider's Susie Neilson.

The air-monitoring devices, which can cost hundreds of dollars each, can provide data on CO2 levels throughout the day, as long as they're exposed to open air, the Times reported. However, some school officials have discouraged the use of the machines, while others have dismissed parents' findings of high CO2 concentrations in their children's classrooms and defended the school buildings' ventilation.

"It's our responsibility to assure every space is safe," Kris Munro, the superintendent of Santa Cruz City Schools, said to the Times. "Not just to have individuals coming on campus to find out: Is a specific place safe?"

But parents have defended the tactic as a way to get insight on an area they feel schools haven't been transparent enough about and as a tool to pressure their children's schools to make changes if ventilation isn't satisfactory.

Read the full story about parents sneaking air quality monitors into school in The New York Times.