diff --git a/src/energenie/Devices.py b/src/energenie/Devices.py
index 9c07b56..5f5d7a2 100644
--- a/src/energenie/Devices.py
+++ b/src/energenie/Devices.py
@@ -277,6 +277,9 @@
         self.capabilities = Capabilities()
         self.updated_cb = None
 
+    def get_config(self):
+        raise RuntimeError("There is no configuration for a base Device")
+
     def has_switch(self):
         return hasattr(self.capabilities, "switch")
 
@@ -353,6 +356,14 @@
     def __repr__(self):
         return "LegacyDevice(%s)" % str(self.device_id)
 
+    def get_config(self):
+        """Get the persistable config, enough to reconstruct this class from a factory"""
+        return {
+            "type":            self.__class__.__name__,
+            "device_id":       self.device_id
+        }
+
+
     def send_message(self, payload):
         #TODO: interface with air_interface
         # Encode the payload two bits per byte as per OOK spec
@@ -388,6 +399,15 @@
         #self.config.encryptPID = CRYPT_PID
         #self.config.encryptPIP = CRYPT_PIP
 
+    def get_config(self):
+        """Get the persistable config, enough to reconstruct this class from a factory"""
+        return {
+            "type":            self.__class__.__name__,
+            "manufacturer_id": self.manufacturer_id,
+            "product_id":      self.product_id,
+            "device_id":       self.device_id
+        }
+
     def __repr__(self):
         return "MiHomeDevice(%s,%s,%s)" % (str(self.manufacturer_id), str(self.product_id), str(self.device_id))
 
diff --git a/src/energenie/Registry.py b/src/energenie/Registry.py
index 53f1dac..094cfa7 100644
--- a/src/energenie/Registry.py
+++ b/src/energenie/Registry.py
@@ -158,7 +158,7 @@
         print("####HERE")
         print(values, type(values))
         """Append a new record to the persistent file"""
-        with open(self.filename, 'w+') as f:
+        with open(self.filename, 'a') as f:
             f.write("ADD %s\n" % key)
             for k in values:
                 v = values[k]
@@ -238,19 +238,7 @@
 
     def add(self, device, name):
         """Add a device class instance to the registry, with a friendly name"""
-        ####HERE
-        #TODO: this is a Device class instance
-        #need to get appropriate data out from it as a map
-        #TODO: This is correct for a MiHomeDevice
-        #but not for a LegacyDevice
-        #TODO: Also, need the class name
-        values = {
-            "type":                Devices.MiHomeDevice, ##TODO MIHO005 ??
-            "manufacturer_id":     device.manufacturer_id,
-            "product_id":          device.product_id,
-            "device_id":           device.device_id
-        }
-        self.store[name] = values
+        self.store[name] = device.get_config()
 
     def get(self, name): # -> Device
         """Get the description for a device class from the store, and construct a class instance"""
diff --git a/src/energenie/Registry_test.py b/src/energenie/Registry_test.py
index 0597cb4..dd6b77c 100644
--- a/src/energenie/Registry_test.py
+++ b/src/energenie/Registry_test.py
@@ -19,6 +19,8 @@
 
     @test_1
     def test_create(self):
+        import os
+        os.unlink('registry.kvs')
         registry = DeviceRegistry("registry.kvs")
 
         # add some devices to the registry, it should auto update the file
@@ -27,7 +29,7 @@
         #Perhaps in Device(), LegacyDevice() and MiHomeDevice() it does this for us
         #and returns a map we can just persist and create from later?
 
-        ##registry.add(Devices.ENER002(device_id=(0xC8C8C, 1)), "fan")
+        registry.add(Devices.ENER002(device_id=(0xC8C8C, 1)), "fan")
 
         # see what the file looks like
         with open(registry.DEFAULT_FILENAME) as f: