diff --git a/FlippR-Driver/include/output/IOutputDriver.h b/FlippR-Driver/include/output/IOutputDriver.h
index cc1d4e6..7d996e3 100644
--- a/FlippR-Driver/include/output/IOutputDriver.h
+++ b/FlippR-Driver/include/output/IOutputDriver.h
@@ -8,6 +8,15 @@
 #ifndef _SRC_OUTPUT_IOUTPUTDRIVER_H_
 #define _SRC_OUTPUT_IOUTPUTDRIVER_H_
 
+#include "output/items/ILamp.h"
+#include "output/items/ISolenoid.h"
+#include "output/items/IDisplay.h"
+#include "output/items/ISound.h"
+
+#include <vector>
+#include <memory>
+#include <boost/optional.hpp>
+
 namespace flippR_driver
 {
 namespace output
@@ -16,8 +25,17 @@ namespace output
 class IOutputDriver
 {
 public:
-	IOutputDriver();
-	virtual ~IOutputDriver();
+	virtual ~IOutputDriver() = default;
+
+	virtual std::vector<std::shared_ptr<items::ILamp>> get_lamps() = 0;
+	virtual std::vector<std::shared_ptr<items::ISolenoid>> get_solenoids() = 0;
+	virtual std::vector<std::shared_ptr<items::ISound>> get_sounds() = 0;
+	virtual std::vector<std::shared_ptr<items::IDisplay>> get_displays() = 0;
+
+	virtual boost::optional<std::shared_ptr<items::ILamp>> get_lamp(std::string name) = 0;
+	virtual boost::optional<std::shared_ptr<items::ISolenoid>> get_solenoid(std::string name) = 0;
+	virtual boost::optional<std::shared_ptr<items::ISound>> get_sound(std::string name) = 0;
+	virtual boost::optional<std::shared_ptr<items::IDisplay>> get_display(char number) = 0;
 };
 
 } /* namespace output */
diff --git a/FlippR-Driver/src/input/EventHandler.h b/FlippR-Driver/src/input/EventHandler.h
index 75ac516..7fd1fcf 100644
--- a/FlippR-Driver/src/input/EventHandler.h
+++ b/FlippR-Driver/src/input/EventHandler.h
@@ -31,7 +31,7 @@ public:
   void handle(Event& event) override;
 
 private:
-  std::shared_ptr<IInputDriver> input_driver;
+  const std::shared_ptr<IInputDriver> input_driver;
 };
 
 }
diff --git a/FlippR-Driver/src/input/EventNotifier.h b/FlippR-Driver/src/input/EventNotifier.h
index 97eb2ac..5245011 100644
--- a/FlippR-Driver/src/input/EventNotifier.h
+++ b/FlippR-Driver/src/input/EventNotifier.h
@@ -42,7 +42,7 @@ private:
   void notify();
 
 private:
-  utility::IBlockingQueue<Event>* event_queue;
+  const utility::IBlockingQueue<Event>* event_queue;
   std::set<IEventHandler*> event_handlers;
 
   bool is_running;
diff --git a/FlippR-Driver/src/output/OutputDriver.h b/FlippR-Driver/src/output/OutputDriver.h
index a522d3f..81e366c 100644
--- a/FlippR-Driver/src/output/OutputDriver.h
+++ b/FlippR-Driver/src/output/OutputDriver.h
@@ -10,14 +10,7 @@
 
 #include "output/IOutputDriver.h"
 
-#include "output/items/ILamp.h"
-#include "output/items/ISolenoid.h"
-#include "output/items/IDisplay.h"
-#include "output/items/ISound.h"
-
-#include <vector>
 #include <map>
-#include <memory>
 
 namespace flippR_driver
 {
@@ -31,21 +24,21 @@ public:
 
   virtual ~OutputDriver() = default;
   // todo what is flipper_relay ?
-  std::vector<std::shared_ptr<items::ILamp>> get_lamps();
-  std::vector<std::shared_ptr<items::ISolenoid>> get_solenoids();
-  std::vector<std::shared_ptr<items::ISound>> get_sounds();
-  std::vector<std::shared_ptr<items::IDisplay>> get_displays();
+  std::vector<std::shared_ptr<items::ILamp>> get_lamps() override;
+  std::vector<std::shared_ptr<items::ISolenoid>> get_solenoids() override;
+  std::vector<std::shared_ptr<items::ISound>> get_sounds() override;
+  std::vector<std::shared_ptr<items::IDisplay>> get_displays() override;
 
-  std::shared_ptr<items::ILamp> get_lamp(std::string name);
-  std::shared_ptr<items::ISolenoid> get_solenoid(std::string name);
-  std::shared_ptr<items::ISound> get_sound(std::string name);
-  std::shared_ptr<items::IDisplay> get_display(char number);
+  boost::optional<std::shared_ptr<items::ILamp>> get_lamp(std::string name) override;
+  boost::optional<std::shared_ptr<items::ISolenoid>> get_solenoid(std::string name) override;
+  boost::optional<std::shared_ptr<items::ISound>> get_sound(std::string name) override;
+  boost::optional<std::shared_ptr<items::IDisplay>> get_display(char number) override;
 
 private:
-  std::map<std::string, std::shared_ptr<items::ILamp>> lamps;
-  std::map<std::string, std::shared_ptr<items::ISolenoid>> solenoids;
-  std::map<char, std::shared_ptr<items::IDisplay>> displays;
-  std::map<std::string, std::shared_ptr<items::ISound>> sounds;
+  const std::map<std::string, std::shared_ptr<items::ILamp>> lamps;
+  const std::map<std::string, std::shared_ptr<items::ISolenoid>> solenoids;
+  const std::map<char, std::shared_ptr<items::IDisplay>> displays;
+  const std::map<std::string, std::shared_ptr<items::ISound>> sounds;
 };
 
 } /* namespace output */