As used in this section and sections twenty-six E and twenty-six F the following terms shall have the following meanings unless the context clearly indicates otherwise:—

1. (a) a distinctive audible trouble signal is given before the battery is incapable of operating the device for alarm purposes, and that such audible trouble signal is produced at least once every minute for seven consecutive days, and
2. (b) the unit is capable of producing an alarm signal for at least four continuous minutes at the battery voltage at which a trouble signal is normally obtained followed by seven days of trouble signal operation, and

3. (c) the monitored batteries meeting these specifications are clearly identified on the unit near the battery compartment.

   1. (a) all power supplies shall be sufficient to operate the alarm signal for at least four continuous minutes, and

   2. (b) all such detector systems shall be installed in accordance with the Massachusetts Electrical Code.

      ''Common hallway'', a common corridor or space separately enclosed which provides common access to the required exitways of the residential building or structure.

      ''Separate sleeping area'', shall mean the area or areas of the dwelling unit in which the bedrooms, or sleeping rooms, are located. Bedrooms, or sleeping rooms, separated by other use areas such as kitchens or living rooms, but not bathrooms, shall be considered as separate sleeping areas.

   ''Approved primary power smoke detector'', shall be a smoke detector which is activated by being permanently wired to a source of alternating current electric power or connected to a source of alternating current electric power by an underwriter's laboratory approved cord with a strain relief and plug retainer; provided, that:

''Approved monitored battery power smoke detector'', shall be a smoke detector which is activated by a battery power source provided that the battery is monitored to assure that the following conditions are met: