In February 2010, a small plane crashed in Palo Alto, Callifornia, killing three people and damaging homes in a residential neighborhood. Months later, The Contra Costa Times obtained audio from a police ShotSpotter device, which captured the sound of the plane crash and the commotion that immediately followed. The audio, on which you can hear people screaming, is embedded above.

The company SST, which sells ShotSpotter technology to police departments, says on its website that "human voices do not trigger ShotSpotter sensors, which are placed in elevated locations in order to enhance their capability as well as ensure citizen privacy." But when loud noises trigger the sensors, the system can and does capture nearby voices.

That's exactly what happened here in Massachusetts, when a ShotSpotter in New Bedford recorded a shouting argument that occurred in the street subsequent to a shooting. The New York Times reports:

In New Bedford, the ShotSpotter recording of the street argument is likely to play a role in the case against two men, Jonathan Flores and Jason Denison, who are charged with murder in the killing of Michael Pina on Dec. 2.

At a bail hearing in January, an assistant district attorney said the system had recorded arguing and yelling on the corner of Dartmouth and Matthew Streets.

Frank Camera, the lawyer for Mr. Flores, said that if the prosecution used the recording as evidence, the issue of privacy could be raised under the state’s wiretapping statute. Mr. Denison’s lawyer, Kathleen Curley, said she planned to file a motion to that effect on behalf of her client.

Mr. Camera said that whether he, too, would argue that the recording constituted a privacy violation depended on what is on the tape.

In one section, he said, a voice can be heard saying “No, Jason! No, Jason!” — a statement that could help his client — but in other parts the words cannot be easily distinguished. He said he was having the tape enhanced to try to clarify it.

In any case, Mr. Camera said, the new technology is “opening up a whole can of worms.”

“If the police are utilizing these conversations, then the issue is, where does it stop?” he said.

Sam Sutter, the district attorney in Bristol County, Mass., called ShotSpotter “an extremely valuable tool” that had helped his office bring charges in four nonfatal shootings.

“In my view legally,” he said, “what is said and picked up by the ShotSpotter recording does not have the expectation of privacy because it’s said out in public, and so I think that will turn out to be admissible evidence.”

James G. Beldock, a vice president at ShotSpotter, said that the system was not intended to record anything except gunshots and that cases like New Bedford’s were extremely rare. “There are people who perceive that these sensors are triggered by conversations, but that is just patently not true,” he said. “They don’t turn on unless they hear a gunshot.”

The machines don't turn on unless they hear a gunshot…or a plane crash. The technology is installed in at least 70 cities throughout the United States, usually in low-income neighborhoods. If you hear a loud noise while you're outside on the street, watch what you say. Someone might be listening.

h/t @OaklandPrivacy