diff --git a/homeassistant/core.py b/homeassistant/core.py
index 03110c6ebec..b9899c5cf25 100644
--- a/homeassistant/core.py
+++ b/homeassistant/core.py
@@ -115,22 +115,23 @@ class StateMachine(object):
         self.eventbus = eventbus
         self.lock = RLock()
 
-    def add_category(self, category, initial_state):
-        """ Add a category which state we will keep track off. """
-        self.states[category] = State(initial_state, datetime.now())
-
     def set_state(self, category, new_state):
-        """ Set the state of a category. """
-        self._validate_category(category)
+        """ Set the state of a category, add category is it does not exist. """
 
         self.lock.acquire()
 
-        old_state = self.states[category]
-
-        if old_state.state != new_state:
+        # Add category is it does not exist
+        if category not in self.states:
             self.states[category] = State(new_state, datetime.now())
 
-            self.eventbus.fire(Event(EVENT_STATE_CHANGED, {'category':category, 'old_state':old_state, 'new_state':self.states[category]}))
+        # Change state and fire listeners
+        else:
+            old_state = self.states[category]
+
+            if old_state.state != new_state:
+                self.states[category] = State(new_state, datetime.now())
+
+                self.eventbus.fire(Event(EVENT_STATE_CHANGED, {'category':category, 'old_state':old_state, 'new_state':self.states[category]}))
 
         self.lock.release()
 
@@ -151,6 +152,7 @@ class StateMachine(object):
         return [(category, self.states[category].state, self.states[category].last_changed) for category in sorted(self.states.keys())]
 
     def _validate_category(self, category):
+        """ Helper function to throw an exception when the category does not exist. """
         if category not in self.states:
             raise CategoryDoesNotExistException("Category {} does not exist.".format(category))
 
diff --git a/homeassistant/observers.py b/homeassistant/observers.py
index 28fe7cb9b8f..0b4c831598c 100644
--- a/homeassistant/observers.py
+++ b/homeassistant/observers.py
@@ -122,7 +122,7 @@ class WeatherWatcher(object):
 
         self.sun = ephem.Sun()
 
-        self._update_sun_state(create_state=True)
+        self._update_sun_state()
 
 
     def next_sun_rising(self, observer=None):
@@ -143,7 +143,7 @@ class WeatherWatcher(object):
         return ephem.localtime(observer.next_setting(self.sun))
 
 
-    def _update_sun_state(self, now=None, create_state=False):
+    def _update_sun_state(self, now=None):
         """ Updates the state of the sun and schedules when to check next. """
 
         observer = self._get_observer()
@@ -161,11 +161,7 @@ class WeatherWatcher(object):
 
         self.logger.info("Sun:{}. Next change: {}".format(new_state, next_change.strftime("%H:%M")))
 
-        if create_state:
-            self.statemachine.add_category(STATE_CATEGORY_SUN, new_state)
-
-        else:
-            self.statemachine.set_state(STATE_CATEGORY_SUN, new_state)
+        self.statemachine.set_state(STATE_CATEGORY_SUN, new_state)
 
         # +10 seconds to be sure that the change has occured
         track_time_change(self.eventbus, self._update_sun_state, point_in_time=next_change + timedelta(seconds=10))
@@ -206,10 +202,10 @@ class DeviceTracker(object):
                 new_last_seen = default_last_seen
 
             self.devices_to_track[device]['last_seen'] = new_last_seen
-            self.statemachine.add_category(self.devices_to_track[device]['category'], new_state)
+            self.statemachine.set_state(self.devices_to_track[device]['category'], new_state)
 
         # Update all devices state
-        statemachine.add_category(STATE_CATEGORY_ALL_DEVICES, DEVICE_STATE_HOME if len(initial_search) > 0 else DEVICE_STATE_NOT_HOME)
+        statemachine.set_state(STATE_CATEGORY_ALL_DEVICES, DEVICE_STATE_HOME if len(initial_search) > 0 else DEVICE_STATE_NOT_HOME)
 
         track_time_change(eventbus, lambda time: self.update_devices(device_scanner.get_active_devices()))
 
diff --git a/homeassistant/test.py b/homeassistant/test.py
index aa05ece11f5..301fba4f411 100644
--- a/homeassistant/test.py
+++ b/homeassistant/test.py
@@ -48,7 +48,7 @@ class TestHTTPInterface(HomeAssistantTestCase):
 
             HTTPInterface(self.eventbus, self.statemachine, API_PASSWORD)
 
-            self.statemachine.add_category("test", "INIT_STATE")
+            self.statemachine.set_state("test", "INIT_STATE")
 
             self.eventbus.fire(Event(EVENT_START))
 
@@ -96,7 +96,8 @@ class TestHTTPInterface(HomeAssistantTestCase):
                                                                     "new_state":"debug_state_change",
                                                                     "api_password":API_PASSWORD})
 
-        self.assertEqual(req.status_code, 400)
+        self.assertEqual(req.status_code, 200)
+        self.assertEqual(self.statemachine.get_state("test_category_that_does_not_exist").state, "debug_state_change")
 
     def test_api_fire_event_with_no_data(self):
         """ Test if the API allows us to fire an event. """