diff --git a/src/mm-modem-base.c b/src/mm-modem-base.c
index af1c6258..890c55c7 100644
--- a/src/mm-modem-base.c
+++ b/src/mm-modem-base.c
@@ -265,6 +265,9 @@ mm_modem_base_init (MMModemBase *self)
     mm_properties_changed_signal_register_property (G_OBJECT (self),
                                                     MM_MODEM_ENABLED,
                                                     MM_MODEM_DBUS_INTERFACE);
+    mm_properties_changed_signal_register_property (G_OBJECT (self),
+                                                    MM_MODEM_UNLOCK_REQUIRED,
+                                                    MM_MODEM_DBUS_INTERFACE);
 }
 
 static void