qgis - How to implement signals on add or modify feature?

I've created a test plug-in in QGIS successfully, but have had a hard time implementing a signal on a vector layer event (add or modify feature). I've add this to my initGUI method:

QObject.connect(self.iface.activeLayer(),SIGNAL("featureAdded(QgsFeatureId)"),self.addedGeometry)

and this definition:

def addedGeometry(self, intValue):
        QMessageBox.information( self.iface.mainWindow(),"Info", "Hi!!!" )

I get the following error when I load my plug-in:

QObject.connect(self.iface.activeLayer(),SIGNAL("featureAdded(QgsFeatureId)"),self.addedGeometry)

TypeError: arguments did not match any overloaded call:
  QObject.connect(QObject, SIGNAL(), QObject, SLOT(), Qt.ConnectionType=Qt.AutoConnection): argument 1 has unexpected type 'NoneType'
  QObject.connect(QObject, SIGNAL(), callable, Qt.ConnectionType=Qt.AutoConnection): argument 1 has unexpected type 'NoneType'
  QObject.connect(QObject, SIGNAL(), SLOT(), Qt.ConnectionType=Qt.AutoConnection): first argument of unbound method must have type 'QObject'

If anyone could help I would be very grateful! I can't find a lot of examples of implementing signals on QGIS objects.