Overriding sync globally.

gistfile1.js

// Overriding sync
var Sync = Backbone.sync;
Backbone.sync = function (method, model, options) {
  var success = options.success;
  var error   = options.error;
  
  // Your custom code goes here, you should be able to access
  // the xhr via options.xhr, or in the second argument from the ajax call.
  options.success = function (resp, status, xhr) {
    success.apply(this, arguments);
    alert("Success with model " + JSON.stringify(model));
  };
  options.error = function (xhr, status, error) {
    error.apply(this, arguments);
    alert("Error with model " + JSON.stringify(model));
  };

  return Sync.call(this, method, model, options);
};