diff --git a/app/domains/design_pattern/observer/employee3.rb b/app/domains/design_pattern/observer/employee3.rb
new file mode 100644
index 0000000..f8eba0f
--- /dev/null
+++ b/app/domains/design_pattern/observer/employee3.rb
@@ -0,0 +1,22 @@
+module DesignPattern
+    module Observer
+        class Employee3
+            include Subject3
+            attr_reader :name
+            attr_accessor :title, :salary
+
+            def initialize(name, title, salary)
+                super()
+                @name = name
+                @title = title
+                @salary = salary
+                @observers = []
+            end
+
+            def salary=(new_salary)
+                @salary = new_salary
+                notify_observers
+            end
+        end
+    end
+end
diff --git a/app/domains/design_pattern/observer/subject3.rb b/app/domains/design_pattern/observer/subject3.rb
new file mode 100644
index 0000000..389dc6b
--- /dev/null
+++ b/app/domains/design_pattern/observer/subject3.rb
@@ -0,0 +1,23 @@
+module DesignPattern
+  module Observer
+    module Subject3
+      def initialize
+        @observers = []
+      end
+
+      def add_observer(&observer)
+        @observers << observer
+      end
+
+      def delete_observer(observer)
+        @observers.delete(observer)
+      end
+
+      def notify_observers
+        @observers.each do |observer|
+          observer.call(self)
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/domains/design_pattern/observer/employee_spec.rb b/spec/domains/design_pattern/observer/employee_spec.rb
index e6d5fec..ae285e4 100644
--- a/spec/domains/design_pattern/observer/employee_spec.rb
+++ b/spec/domains/design_pattern/observer/employee_spec.rb
@@ -65,3 +65,22 @@
     end
   end
 end
+
+describe DesignPattern::Observer::Employee3 do
+  describe '#salary' do
+    it 'observe payroll' do
+      fred = DesignPattern::Observer::Employee3.new('Fred', 'Crane Operator', 30000)
+      fred.add_observer do |change_employee|
+        puts("Cut a new check for #{change_employee.name}!")
+        puts("His salary is now #{change_employee.salary}!")
+      end
+
+      expected = <<-EOS
+Cut a new check for Fred!
+His salary is now 35000!
+      EOS
+
+      expect { fred.salary = 35000 }.to output(expected).to_stdout
+    end
+  end
+end
\ No newline at end of file