"Throughout his career, Officer Hartman has received many letters of recognition and commendation," Chief Michael Lombardo said at the ceremony.
He was named Officer of the Year in 2011 and received three lifesaving awards in 2004, 2008 and 2013, Lombardo said.
Police commission member David Waters praised Hartman's promotion.
"We're delighted with this and we think it is a great choice," he said.
After he was sworn in by Assistant Town Clerk Ann Fiteni, Hartman's wife Lisa pinned the sergeant's badge on her husband's uniform.
The couple have three children: Kaitlyn, 9, Connor, 7, and Ryan, 5.
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