Chief Ron Glidden along with Atty John M. Collins writes a book called "Law Enforcement Guide to Firearms Law", sub-titled "A practical guide for police on Massachusetts and federal firearms law." The book is revised annually with any updates. [It is used in the Police Academy (known as POST in most states, MA is different :icon_neutral: ) to train police officers, chiefs and those that issue firearms licenses.]
Chapter 140: Section 131L. Weapons stored or kept by owner; inoperable by any person other than owner or lawfully authorized user; punishment
Section 131L. (a) It shall be unlawful to store or keep any firearm, rifle or shotgun including, but not limited to, large capacity weapons, or machine gun in any place unless such weapon is secured in a locked container or equipped with a tamper-resistant mechanical lock or other safety device, properly engaged so as to render such weapon inoperable by any person other than the owner or other lawfully authorized user. For purposes of this section, such weapon shall not be deemed stored or kept if carried by or under the control of the owner or other lawfully authorized user.
Criteria for Storage: There is no criteria for storage other than that the gun stored or kept must be secured in a locked container or equipped with a tamper proof locking device. This means that a soft case with a padlock meets the criteria just as well as an expensive gun safe. Likewise a trigger lock (no requirement for it to be state approved) or cable lock will serve as well as a locked cabinet. Also, glass front furniture style gun cabinets are acceptable providing they are capable of being locked.
Other Locked Containers: Many questions have arisen regarding locked rooms. The Executive Office of Public Safety has stated that a locked room that prohibits unauthorized access will meet the criteria for a locked container. However, a person can not lock his house and consider the entire house a locked container.