public class DatabaseChangeListener
{
  #region Constructor

 public DatabaseChangeListener(string connectionString)
 {
  this.connectionString = connectionString;
  SqlDependency.Stop(connectionString);
  SqlDependency.Start(connectionString);
  connection = new SqlConnection(connectionString);
 }

 #endregion Constructor

 # region Finalizer

  ~DatabaseChangeListener()
 {
  SqlDependency.Stop(connectionString);
 }

 #
 endregion Finalizer

 # region Properties

 private readonly string connectionString;
 private readonly SqlConnection connection;

 public delegate void NewMessage();
 public event NewMessage OnChange;

 #endregion Properties

 #region Methods

 public DataTable Start(string changeQuery)
 {
  using(SqlCommand cmd = new SqlCommand(changeQuery, connection) {Notification = null})
  {
   SqlDependency dependency = new SqlDependency(cmd);
   dependency.OnChange += NotifyOnChange;
   if (connection.State == ConnectionState.Closed)
   {
    connection.Open();
   }
   using(DataTable dt = new DataTable())
   {
    dt.Load(cmd.ExecuteReader(CommandBehavior.CloseConnection));
    return dt;
   }
  }
 }

 void NotifyOnChange(object sender, SqlNotificationEventArgs e)
 {
  var dependency = sender as SqlDependency;
  if (dependency != null) dependency.OnChange -= NotifyOnChange;
  if (OnChange != null)
  {
   OnChange();
  }
 }

 #endregion Methods

}