Edit in JSFiddle

(function($){
	$.fn.extend({
            /**
             * Function to determine an action when the user
             * stops press a key in a DOM Object
             * useful for example (searchers) to not send 
             * a query every time the user press a key, instead
             * this will do the action after of a keypress with 
             * a given or default time.
             * 
             * @param {function} funcion
             * @param {integer} tiempo
             * @returns {undefined}
             */
            onstopwrite : function(funcion,tiempo){
                var timerEscritura;
                
                if(!tiempo){
                    tiempo = 400;
                } 
                
                this.keyup(function(e){
                    clearTimeout(timerEscritura);
                    timerEscritura = setTimeout(
                        function(){
                            funcion(tiempo);
                        },
                        tiempo
                    );
                });
            }
        });
})(jQuery);

$(document).ready(function(){
	$('#test').onstopwrite(function(){
  	alert("Sending request");
  },1000); // every second
});

<span>Do something after 1 second, when the user writes.</span>
<input type="text" id="test" />