Somerville has established a new policy aimed at requiring transparency in its use of surveillance technology. The executive order signed by Mayor Joseph A. Curtatone with the support of the Police Department is aimed at protecting individual rights while preserving public safety. “Privacy and civil liberty protections are critical to a free democracy. That’s why this policy introduces checks and balances designed to keep the public safe from crime as well as from privacy and rights violations,” Curtatone said in a prepared statement. Somerville joined with 19 other cities and two states in working with the American Civil Liberties Union to develop policies in their jurisdictions. City officials said they believe Somerville is the first community in Massachusetts. The policy requires a multistep process before new surveillance technology may be purchased and deployed in the city. It includes exceptions for emergency police investigations or public safety needs.John Laidler can be reached at email@example.com.