Westbury received a minority equity stake in A+ Technology in the deal, which was finalized in December. The size of the ownership stake was not disclosed.
A+ Technology chief executive David Antar said the 14-year-old company began meeting with Westbury last October to discuss a deal.
Richard Sicoli, chief financial officer of Westbury Partners, said he was impressed with the company's accomplishments to date: "They weren't a start-up, they were a company that had achieved a critical mass." He noted A+ Technology is the first Long Island business in which his firm has taken equity.
Westbury, which has been investing since 1995 and focuses on tech companies, is a licensed small business investment company and receives a portion of its funds from the federal government. Its current fund manages $200 million in assets.
A+ Technology will use the capital to expand its 40-employee workforce by adding 30 staffers in marketing, sales and engineering in the next year, Antar said.
The company will also build a 24/7 "command center" to provide visual monitoring for its customers in case of emergencies. The investment represents a "significant amount based on our annual revenues," Antar said.
The funding comes amid a dry period for venture capital on Long Island.
Not counting Westbury Partners' stake in A+ Technology, Long Island received about $20 million in venture investments in 2012, for four businesses -- compared to $45 million in 2011, according to the quarterly MoneyTree report published by PricewaterhouseCoopers and the National Venture Capital Association.
Among the four businesses, Stony Brook biotech company Coferon Inc. also received $12 million in venture capital, last summer.
A+ Technology provides security systems to towns and businesses on Long Island, including MacArthur Airport in Ronkonkoma. Most of the company's clients are in New York, but Antar said he hopes to use the new capital to expand more into the tri-state area.
The company also focuses a majority of its business in school security and surveillance, which has become a hot-button issue since the Dec. 14 shooting at Sandy Hook Elementary School in Newtown, Conn., that claimed the lives of 20 students and six educators. Antar said when the tragedy occurred at Sandy Hook, A+ Technology and Westbury Partners were already deep in negotiations, but the events "did show a justification of what we do and why it's . . . critical to provide a secure and safe environment for security and staff."