Before the sale of a home in Massachusetts the local fire department has to come in and verify that there are adequate smoke and carbon monoxide detectors in the home. These certifications are usually good for 90 days. My advice as an agent is to get them in early. Many agents wait until the last minute and fire departments can’t go out for as long as 3 weeks.
This is a good reference tool for both sellers and listing agents.
Massachusetts guide for smoke and carbon monoxide detectors (PDF printer friendly version)