If Massachusetts, it is the sellers responsibility to outfit the home with approved smoke detectors & carbon monoxide detectors. It is further the sellers obligation to obtain a compliance certificate from the local fire department prior to closing.
However, when working with Buyers of bank owned(REO) and foreclosed property, I frequently encounter property listings that disclose it is the Buyer’s responsibility to obtain the smoke & CO compliance certificate.
Most REO purchase contracts include this language because the property is being sold “as-is”.
Inexperienced agents may simply let this go, but I like to take fight back. I recommend that my clients write offers that clearly articulate that the smoke & carbon monoxide detectors and the corresponding compliance certificate shall remain the responsibility of the Seller. Some agents object, but if the Buyer’s offer is strong and well-qualified, most listing agents will submit to this request with an offer.
Mark J. Kiklis, REALTOR® at Kiklis Real Estate, LLC Follow Mark on Twitter
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Real Estate, Real Problems 
Good point, get the bank to step up – the other information to consider if you are responsible is that technology requirements have changed over the years for smoke detector type and location – here is a link to a past blog I wrote on that subject: http://westford.patch.com/blog_posts/new-massachusetts-smoke-detector-requirements
Enjoy the day!
Bill