Suffolk Police Commissioner Timothy Sini announced Monday the department has placed a network of a dozen overt surveillance cameras across the county in trouble spots as both a crime deterrent and investigative tool.

“The message here is think twice before doing something illegal, think twice before doing something that erodes the quality of life for our residents, because we are watching,” said Sini, as he stood at the intersection of Broadway and Rockne Street in Greenlawn, where residents said crime is frequent.

The 12 cameras, purchased with $130,000 in asset forfeiture funds, have been distributed to the department’s seven police precincts. The number of cameras could eventually increase based on need, said Sini, who is a candidate for Suffolk County district attorney.

Some said they had for years asked the police to do more to crack down on illegal activity, citing robberies of the corner deli.

Walter Springsteen, 60, called his Greenlawn neighborhood a “high-crime area” and said: “It’s overdue. This area has been plagued for a very long time with crime of various sorts, we have drugs,theft, vandalism. If this will help abate that, I couldn’t be happier.”

Sini said statistics show violent crime year-to-date compared with last year is down 15.9 percent, property crime down 11 percent and all crime decreased over 10 percent.

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Suffolk Legis. William Spencer (D-Centerport), who along with Deputy Police Commissioner John Barry, joined Sini, said the cameras could decrease gang activity.

The mobile cameras allow precinct-level supervisors to move them based on crime statistics and community feedback, Sini said. The Wi-Fi-based cameras are monitored by detectives and can be assessed by any police officer on in-car computers and mobile devices, Sini said, adding that 2017 is “the year of technology” for the police department.”

In response, the Twitter account for the New York Civil Liberties Union, which has expressed privacy concerns over the use of police cameras, tweeted: “Hope it’s also the year of transparency.”

Asked about privacy, Sini said: “It says ‘Suffolk County Police’ on the cameras. So it’s not private surveillance, right? This is a program that we’re advertising, that we want people to know about. And it’s only going to be in public, where folks don’t enjoy any reasonable expectation of privacy.”