title: Linq to make sure that no two objects have same property value
body: <p>I've a class called Alarm with a property called Description.</p>
  
  <pre><code>public class Alarm
  {
      public string Description { get; set; }
  }
  </code></pre>
  
  <p>In a list of Alarms, I've to make sure that no two Alarm in the list have same Description.</p>
  
  <p>I want to use linq to do this check and <strong>get a list of alarms with duplicate description</strong>.</p>