As of January 1, 2018 regardless of when a property was built, smoke alarms are a key part of every sale.
All battery operated only alarms must be powered by 10-year sealed batteries, and no unit, whether battery operated or AC, may be older than 10 years.
Types of alarms found in homes have changed over time based on requirements at the time of construction. Hardwired AC Alarms must be replaced with hardwired alarms of the same type.
• Additional alarms required as of January 1, 2018 (such as in basement) may be battery operated if they are 10-year sealed battery alarms with a silence/hush button feature.
• A seller who fails to comply with the law is subject to a fine,imprisonment, or both.
• As required by law, any information about alarms that is shared with a REALTOR® is considered a material fact that must be disclosed to all parties.
This link from MD Realtors gives you a detailed breakdown. Enjoy!