diff --git a/Components/DiskII/DiskII.cpp b/Components/DiskII/DiskII.cpp
index da897c36c..373c5ccf6 100644
--- a/Components/DiskII/DiskII.cpp
+++ b/Components/DiskII/DiskII.cpp
@@ -236,3 +236,7 @@ uint8_t DiskII::trigger_address(int address, uint8_t value) {
 	return 0xff;
 }
 
+void DiskII::set_activity_observer(Activity::Observer *observer) {
+	drives_[0].set_activity_observer(observer, "Drive 1", true);
+	drives_[1].set_activity_observer(observer, "Drive 2", true);
+}
diff --git a/Components/DiskII/DiskII.hpp b/Components/DiskII/DiskII.hpp
index fd37e9353..37e083ef8 100644
--- a/Components/DiskII/DiskII.hpp
+++ b/Components/DiskII/DiskII.hpp
@@ -15,6 +15,8 @@
 #include "../../Storage/Disk/Disk.hpp"
 #include "../../Storage/Disk/Drive.hpp"
 
+#include "../../Activity/Observer.hpp"
+
 #include <array>
 #include <cstdint>
 #include <vector>
@@ -40,6 +42,8 @@ class DiskII:
 		void set_disk(const std::shared_ptr<Storage::Disk::Disk> &disk, int drive);
 		bool is_sleeping() override;
 
+		void set_activity_observer(Activity::Observer *observer);
+
 	private:
 		enum class Control {
 			P0, P1, P2, P3,
diff --git a/Machines/AppleII/AppleII.cpp b/Machines/AppleII/AppleII.cpp
index f75655762..85eccd9ec 100644
--- a/Machines/AppleII/AppleII.cpp
+++ b/Machines/AppleII/AppleII.cpp
@@ -8,6 +8,7 @@
 
 #include "AppleII.hpp"
 
+#include "../../Activity/Source.hpp"
 #include "../ConfigurationTarget.hpp"
 #include "../CRTMachine.hpp"
 #include "../KeyboardMachine.hpp"
@@ -24,6 +25,7 @@
 
 #include "../../Analyser/Static/AppleII/Target.hpp"
 
+#include <array>
 #include <memory>
 
 namespace {
@@ -34,7 +36,8 @@ class ConcreteMachine:
 	public KeyboardMachine::Machine,
 	public CPU::MOS6502::BusHandler,
 	public Inputs::Keyboard,
-	public AppleII::Machine {
+	public AppleII::Machine,
+	public Activity::Source {
 	private:
 		struct VideoBusHandler : public AppleII::Video::BusHandler {
 			public:
@@ -62,8 +65,8 @@ class ConcreteMachine:
 			speaker_.run_for(audio_queue_, cycles_since_audio_update_.divide(Cycles(audio_divider)));
 		}
 		void update_cards() {
-			for(int c = 0; c < 7; ++c) {
-				if(cards_[c]) cards_[c]->run_for(cycles_since_card_update_, stretched_cycles_since_card_update_);
+			for(const auto &card : cards_) {
+				if(card) card->run_for(cycles_since_card_update_, stretched_cycles_since_card_update_);
 			}
 			cycles_since_card_update_ = 0;
 			stretched_cycles_since_card_update_ = 0;
@@ -80,7 +83,7 @@ class ConcreteMachine:
 		Cycles cycles_since_audio_update_;
 
 		ROMMachine::ROMFetcher rom_fetcher_;
-		std::unique_ptr<AppleII::Card> cards_[7];
+		std::array<std::unique_ptr<AppleII::Card>, 7> cards_;
 		Cycles cycles_since_card_update_;
 		int stretched_cycles_since_card_update_ = 0;
 
@@ -372,6 +375,13 @@ class ConcreteMachine:
 			}
 			return true;
 		}
+
+		// MARK: Activity::Source
+		void set_activity_observer(Activity::Observer *observer) override {
+			for(const auto &card: cards_) {
+				if(card) card->set_activity_observer(observer);
+			}
+		}
 };
 
 }
diff --git a/Machines/AppleII/Card.hpp b/Machines/AppleII/Card.hpp
index d7c00cdb6..de89bb75e 100644
--- a/Machines/AppleII/Card.hpp
+++ b/Machines/AppleII/Card.hpp
@@ -11,6 +11,7 @@
 
 #include "../../Processors/6502/6502.hpp"
 #include "../../ClockReceiver/ClockReceiver.hpp"
+#include "../../Activity/Observer.hpp"
 
 namespace AppleII {
 
@@ -21,6 +22,9 @@ class Card {
 
 		/*! Performs a bus operation; the card is implicitly selected. */
 		virtual void perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) = 0;
+
+		/*! Supplies a target for observers. */
+		virtual void set_activity_observer(Activity::Observer *observer) {}
 };
 
 }
diff --git a/Machines/AppleII/DiskIICard.cpp b/Machines/AppleII/DiskIICard.cpp
index b0941b28e..527b23b39 100644
--- a/Machines/AppleII/DiskIICard.cpp
+++ b/Machines/AppleII/DiskIICard.cpp
@@ -40,3 +40,7 @@ void DiskIICard::run_for(Cycles cycles, int stretches) {
 void DiskIICard::set_disk(const std::shared_ptr<Storage::Disk::Disk> &disk, int drive) {
 	diskii_.set_disk(disk, drive);
 }
+
+void DiskIICard::set_activity_observer(Activity::Observer *observer) {
+	diskii_.set_activity_observer(observer);
+}
diff --git a/Machines/AppleII/DiskIICard.hpp b/Machines/AppleII/DiskIICard.hpp
index 7f03d0ddc..849e37f94 100644
--- a/Machines/AppleII/DiskIICard.hpp
+++ b/Machines/AppleII/DiskIICard.hpp
@@ -24,8 +24,11 @@ namespace AppleII {
 class DiskIICard: public Card {
 	public:
 		DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sector);
+
 		void perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) override;
 		void run_for(Cycles cycles, int stretches) override;
+		void set_activity_observer(Activity::Observer *observer) override;
+
 		void set_disk(const std::shared_ptr<Storage::Disk::Disk> &disk, int drive);
 
 	private: