“We called it Mini Coachella,” recounts Dave Krauss, who once managed many short-term rental units. One weekend, a tenant checked into one of his apartments. Then they threw a raucous, weekend-long party complete with live music. “My neighbors weren’t invited, but they had tickets, in a way.”

It wasn’t until two days later that Krauss heard about it–from a lawyer. Like many property managers, Krauss didn’t live on site, so he had no clue. But that didn’t mean he wanted to be a bad neighbor. The situation inspired Krauss to call his friend, electrical engineer and software programmer Andrew Schulz. Together, the duo founded NoiseAware.

The company launched about a year ago, aiming its noise-tracking hardware and software platform primarily at property management companies with the tagline “a smoke detector for noise.” But in truth, the entire service they’ve built is far more clever than that. NoiseAware is capable of distinguishing noise from true nuisance, and alerting landlords with a text message only when things are out of hand. Landlords can also log into an online dashboard to track noise trends over time. By utilizing inexpensive sensor technology, NoiseAware is targeting an age-old problem of urban life.

Noise can feel like an assault on your ears, even if it’s generally not malicious. New York City, for instance, fielded 420,000 calls to 311 last year complaining about noise. Fifty percent were either partying–not a huge surprise–or simply loud talking, which is more the product of humanity being stacked atop itself than anything else. Even still, noise continues to be the biggest single complaint on N.Y.C.’s 311.

At NoiseAware’s core is hardware: Simple decibel sensors that plug into the wall and connect to a Wi-Fi network. They’re installed in any apartment being monitored, placed only in spots that tend to get loud, like a living room where a TV or stereo might be blaring. Crucially, however, they don’t infringe upon privacy. Unlike an Amazon Echo or Google Home, they don’t have the processing power to detect speech.

“We cannot interpret language by design, and do not. We measure decibel noise levels . . . not content,” says Krauss. “That was the number-one design consideration.”

But these dumb ears are always listening. And over time, they create longitudinal trends for noise. Unlike your average smoke detector, which will needlessly sound the alarm anytime you turn your oven too high, NoiseAware can distinguish a real noise disturbance (like a party) from a random accident (like dropping some pans). Plus, it can recognize if some random renter has cranked the music just a bit louder than most, and measure that it’s gone on a few minutes too long. Only then does it text the owner with an alert that they should contact their renter.