Grunt 'watch' command not working

I have noticed there have been several questions floating around regarding grunt watch however I tried to run the watch task by grunt in the command line but it doesn't work for me. My terminal doesn't seem to be picking any changes.

i'm not sure if it is my file structure or the set up of my files.. below is an example. Can anyone let me know what i have done wrong?

   sass: {
        dist: {
            options: {
                style: 'compressed',
                require: 'susy'
            },
            files: {
                'app/styles/css/main.css': 'app/styles/sass/main.scss'
            }
        }
    },

    css: {
        files: ['css/*.scss'],
        tasks: ['sass'],
        options: {
            spawn: false,
        }

    },
     watch: {

        css: {
            files: 'app/styles/sass/*.scss',
            tasks: ['sass'],
            options: {
                livereload: true,
            },
        }

    }

});


grunt.loadNpmTasks('grunt-contrib-sass');
grunt.loadNpmTasks('grunt-contrib-watch');
grunt.loadNpmTasks('grunt-autoprefixer');
grunt.loadNpmTasks('grunt-contrib-cssmin');
grunt.loadNpmTasks('grunt-contrib-watch');
grunt.loadNpmTasks('grunt-sprite-generator');
grunt.registerTask('watchfiles', ['sass',  'watch' ]);