Thanks to the Harford County Volunteer Fire & EMS Association for the reminder:
As of July 1, 2013, homeowners with battery-powered smoke alarms must update to long-life sealed-in battery smoke alarms. This law applies to homes with alarms more than 10 years old. Additionally, homes will be required to install smoke alarms in all sleeping areas. Sealed-in battery alarms may be used in those locations if the home currently has hardwired alarms.
If you have any questions about this law, please contact your local fire department for more information.