Best way to detect a release build from a debug build? .net

Specifically, like this in C#:

#if (DEBUG)
   Debug Stuff
#endif

C# has the following preprocessor directives:

#if 
#else 
#elif // Else If
#endif
#define
#undef // Undefine
#warning // Causes the preprocessor to fire warning
#error // Causes the preprocessor to fire a fatal error
#line // Lets the preprocessor know where this source line came from
#region // Codefolding
#endregion 

  if (System.Diagnostics.Debugger.IsAttached)
  {
           // Do this
  }
  else
  {
            // Do that
  }

I should had used google.

#if DEBUG
    Console.WriteLine("Debug mode.") 
#else 
    Console.WriteLine("Release mode.") 
#endif 

Make sure that the option "Configuration settings" -> "Build" "Define DEBUG constant" in the project properties is checked.