Massachusetts Law About Carbon Monoxide Detectors
The Law
Nicole's Law: MGL c.148, s.26F 1/2. Law effective March 31, 2006 requires carbon monoxide detectors in homes. The law is named for 7-year-old Nicole Garofalo who died in January 2005 when a heating vent in her house was blocked by snow drifts, allowing carbon monoxide to accumulate in the home.
Massachusetts Regulations
527 CMR 31: Carbon Monoxide Alarms
Other Web Sources
Carbon Monoxide Detector Law Explained, Donahue and Grolman.. Brief podcast explains the basics of Nicole's Law. 
Carbon Monoxide Safety, Mass. Dept. of Fire Services. Explains the requirements of the new Carbon Monoxide Detector Law (Nicole's Law) and regulations. Links to everything you need to know about the law.
An Introduction to Indoor Air Quality: Carbon Monoxide, US Environmental Protection Agency. Explains the sources, dangers and remediation of carbon monoxide.
Print Sources
Handling Residential Real Estate Transactions in Massachusetts, MCLE loose-leaf, chapter 4.2.