diff --git a/spybug/aaa_config.hh b/spybug/aaa_config.hh
index d33e71e..19d1ca1 100644
--- a/spybug/aaa_config.hh
+++ b/spybug/aaa_config.hh
@@ -24,6 +24,8 @@
 #define TIMER_COMPARE 1000 /* 16MHz / 1000 = 16kHz. */
 #define FLUSH_SAMPLES 64000 /* Flush WAV file every n samples. */
 #define PIN_SS 10
+
+#define REC_FILE_FMT "REC_%03u.WAV" /* Must be all caps; must use %u in some form exactly once. */
 /**********************
  END USER CONFIGURATION
  **********************/
diff --git a/spybug/cmd.cpp b/spybug/cmd.cpp
new file mode 100644
index 0000000..f3f7838
--- /dev/null
+++ b/spybug/cmd.cpp
@@ -0,0 +1,191 @@
+// Copyright 2022 Darwin Schuppan <darwin@nobrain.org>
+// SPDX license identifier: MIT
+
+#include "cmd.hh"
+
+#include <Arduino.h>
+#include <SD.h>
+
+#include "aaa_config.hh"
+#include "fstr.hh"
+#include "io.hh"
+#include "settings.hh"
+#include "sys.hh"
+
+static bool sd_initialized = false;
+
+static void try_init_sd() {
+	if (sd_initialized)
+		return;
+	printf(F("Initializing SD card..."));
+	#ifdef PIN_COMPONENT_SWITCH
+		digitalWrite(PIN_COMPONENT_SWITCH, COMPONENT_SWITCH_ON);
+		delay(500); /* Wait for components to initialize. */
+	#endif
+	if (SD.begin(PIN_SS)) {
+		printf(F("Done.\n"));
+		sd_initialized = true;
+	} else
+		printf(F("\nError initializing SD card.\n"));
+}
+
+static void sd_error() {
+	printf(F("Error reading from SD card.\n"));
+	sd_initialized = false;
+}
+
+static void command_loop() {
+	// Process Commands
+	if (Serial.available()) {
+		char args[6][20];
+		size_t len = 0;
+		size_t n_args = 0;
+		int c = getchar();
+		while (c != '\n' && n_args < 4) {
+			if (c == ' ')
+				c = getchar();
+			else {
+				do {
+					args[n_args][len++] = c;
+					c = getchar();
+				} while (c != ' ' && c != '\n' && len < 20-1);
+				args[n_args][len] = 0;
+				len = 0;
+				n_args++;
+			}
+		}
+		if (n_args >= 1) {
+			if (fstreq(args[0], F("set"))) {
+				if ((n_args == 3 || n_args == 4) && fstreq(args[1], F("wait"))) {
+					float n = atof(args[2]);
+					unsigned long mins;
+					if (n_args == 4 && (fstreq(args[3], F("hours")) || fstreq(args[3], F("hour"))))
+						mins = 60.f * n;
+					else
+						mins = n;
+					settings.recording_delay = mins;
+					settings.save();
+					printf(F("Set waiting time to %lu minutes or "), settings.recording_delay);
+					print_special((float)settings.recording_delay / 60.f);
+					printf(F(" hours.\n"));
+				} else if (n_args == 3 && fstreq(args[1], F("serial"))) {
+					if (fstreq(args[2], F("on"))) {
+						settings.serial_log = true;
+						settings.save();
+						printf(F("Serial log enabled.\n"));
+					} else if (fstreq(args[2], F("off"))) {
+						settings.serial_log = false;
+						settings.save();
+						printf(F("Serial log disabled.\n"));
+					} else {
+						printf(F("Usage: 'set serial [on|off]'.\n"));
+					}
+				} else {
+					printf(F("Usage: 'set wait <number> [minutes|hours]' or 'set serial [on|off]'.\n"));
+				}
+			} else if (fstreq(args[0], F("get"))) {
+				if (n_args == 2 && fstreq(args[1], F("wait"))) {
+					printf(F("Current waiting time: %lu minutes or "), settings.recording_delay);
+					print_special((float)settings.recording_delay / 60.f);
+					printf(F(" hours.\n"));
+				} else {
+					printf(F("Usage: 'get wait'.\n"));
+				}
+			} else if (fstreq(args[0], F("sd"))) {
+				try_init_sd();
+				if (sd_initialized) {
+					if (n_args == 2 && fstreq(args[1], F("list"))) {
+						File root = SD.open("/");
+						if (root) {
+							printf(F("Files:\n"));
+							bool files = false;
+							size_t cols = 0;
+							while (1) {
+								File entry = root.openNextFile();
+								if (!entry)
+									break;
+								files = true;
+								if (cols >= 3) {
+									cols = 0;
+									printf(F("\n"));
+								}
+								printf(F("  %s"), entry.name());
+								cols++;
+								entry.close();
+							}
+							if (!files)
+								printf(F("[NONE]"));
+							printf(F("\n"));
+						} else
+							sd_error();
+						root.close();
+					} else if (n_args == 3 && fstreq(args[1], F("remove"))) {
+						if (SD.remove(args[2]))
+							printf(F("Deleted '%s'."), args[2]);
+						else
+							printf(F("Error removing '%s'."), args[2]);
+					} else if (n_args == 2 && fstreq(args[1], F("remove_all"))) {
+						File root = SD.open("/");
+						if (root) {
+							printf(F("Deleted:\n"));
+							bool deleted = false;
+							size_t cols = 0;
+							while (1) {
+								File entry = root.openNextFile();
+								if (!entry)
+									break;
+								const char *name = entry.name();
+								unsigned int garbage;
+								if (!entry.isDirectory() && sscanf(name, REC_FILE_FMT, &garbage) == 1) {
+									if (cols >= 3) {
+										cols = 0;
+										printf(F("\n"));
+									}
+									deleted = true;
+									SD.remove(name);
+									printf(F("  %s"), name);
+									cols++;
+								}
+								entry.close();
+							}
+							if (!deleted)
+								printf(F("[NONE]"));
+							printf(F("\n"));
+						} else
+							sd_error();
+						root.close();
+					} else if (n_args != 1) {
+						printf(F("Usage: 'sd list', 'sd remove <filename>' or 'sd remove_all'.\n"));
+					}
+				}
+			} else if (fstreq(args[0], F("help"))) {
+				printf(F("Commands:\n"));
+				printf(F("  help                               --  Display this page.\n"));
+				printf(F("  exit                               --  Leave command mode.\n"));
+				printf(F("  get wait                           --  Display current delay setting.\n"));
+				printf(F("  set wait <number> [minutes|hours]  --  Change current delay setting.\n"));
+				printf(F("  set serial [on|off]                --  Write log to serial output.\n"));
+				printf(F("  sd                                 --  Initialize the SD card.\n"));
+				printf(F("  sd list                            --  List file on SD card.\n"));
+				printf(F("  sd remove <filename>               --  Delete a file from SD card.\n"));
+				printf(F("  sd remove_all                      --  Delete all recordings from SD card.\n"));
+			} else if (fstreq(args[0], F("exit"))) {
+				printf(F("Bye!\n"));
+				Serial.flush();
+				full_reset();
+			} else
+				printf(F("Invalid command: '%s'. Type 'help' for a list of commands.\n"), args[0]);
+		} else {
+			printf(F("Please specify a command. Type 'help' for a list of commands.\n"));
+		}
+	}
+}
+
+void cmd() {
+	printf(F("You are now in command mode. Reset to exit. Type 'help' for a list of commands.\n"));
+	while (Serial.available()) Serial.read();
+	while (1) {
+		command_loop();
+		delay(50);
+	}
+}
diff --git a/spybug/cmd.hh b/spybug/cmd.hh
new file mode 100644
index 0000000..455c6f0
--- /dev/null
+++ b/spybug/cmd.hh
@@ -0,0 +1,6 @@
+// Copyright 2022 Darwin Schuppan <darwin@nobrain.org>
+// SPDX license identifier: MIT
+
+#pragma once
+
+void cmd();
diff --git a/spybug/io.hh b/spybug/io.hh
index a77b0e9..ddb6433 100644
--- a/spybug/io.hh
+++ b/spybug/io.hh
@@ -6,3 +6,9 @@
 #include <Arduino.h>
 
 void io_setup();
+
+#define print_special(x) { Serial.print(x); }
+#define die(fmt, ...) { disable_recording_interrupts(); if (settings.serial_log) { printf(F("Fatal: ")); printf(fmt, ##__VA_ARGS__); Serial.flush(); } while(1); }
+#define dbg(fmt, ...) { printf(F("Debug: ")); printf(fmt, ##__VA_ARGS__); }
+#define info(fmt, ...) { if (settings.serial_log) printf(fmt, ##__VA_ARGS__); }
+#define info_special(x) { if (settings.serial_log) Serial.print(x); }
diff --git a/spybug/settings.cpp b/spybug/settings.cpp
new file mode 100644
index 0000000..56fd2e8
--- /dev/null
+++ b/spybug/settings.cpp
@@ -0,0 +1,6 @@
+// Copyright 2022 Darwin Schuppan <darwin@nobrain.org>
+// SPDX license identifier: MIT
+
+#include "settings.hh"
+
+EEPROM_Settings_Class settings;
diff --git a/spybug/settings.hh b/spybug/settings.hh
index bcd065a..1c1b5af 100644
--- a/spybug/settings.hh
+++ b/spybug/settings.hh
@@ -13,3 +13,5 @@ struct EEPROM_Settings_Class {
 	inline void load() { EEPROM.get(EEADDR_SETTINGS, *this); }
 	inline void save() { EEPROM.put(EEADDR_SETTINGS, *this); }
 };
+
+extern EEPROM_Settings_Class settings;
diff --git a/spybug/spybug.ino b/spybug/spybug.ino
index b8afe13..ca458b8 100644
--- a/spybug/spybug.ino
+++ b/spybug/spybug.ino
@@ -30,68 +30,18 @@
 
 #include <SD.h>
 #include <SPI.h>
-#include <avr/interrupt.h>
-#include <avr/io.h>
-#include <avr/wdt.h>
-#include <avr/sleep.h>
 
 #include "aaa_config.hh"
+#include "cmd.hh"
 #include "fstr.hh"
 #include "io.hh"
 #include "settings.hh"
+#include "sys.hh"
 
 #if !defined(__AVR_ATmega328P__) || F_CPU != 16000000
 #error "This program only works on ATmega328P devices with a clock frequency of 16MHz!"
 #endif
 
-void (*full_reset)() = nullptr;
-
-#define print_special(x) { Serial.print(x); }
-#define die(fmt, ...) { disable_recording_interrupts(); if (settings.serial_log) { printf(F("Fatal: ")); printf(fmt, ##__VA_ARGS__); Serial.flush(); } while(1); }
-#define dbg(fmt, ...) { printf(F("Debug: ")); printf(fmt, ##__VA_ARGS__); }
-#define info(fmt, ...) { if (settings.serial_log) printf(fmt, ##__VA_ARGS__); }
-#define info_special(x) { if (settings.serial_log) Serial.print(x); }
-
-volatile bool wdt_int_sleep_mode = false;
-ISR (WDT_vect) {
-	if (wdt_int_sleep_mode)
-		wdt_disable();
-	else
-		full_reset();
-}
-
-/* Based on https://github.com/rocketscream/Low-Power. */
-static void low_power_sleep_minutes(unsigned long t) {
-	wdt_int_sleep_mode = true;
-	ADCSRA &= ~_BV(ADEN); /* Disable ADC. */
-	for (unsigned long i = 0; 8ul * i < 60ul * t; i++) {
-		// Power Down for 8s
-		wdt_enable(WDTO_8S);   /* Start watchdog timer for 8s. */
-		WDTCSR |= (1 << WDIE); /* Enable watchdog interrupt. */
-		do {
-			set_sleep_mode(SLEEP_MODE_PWR_DOWN);
-			cli();
-			sleep_enable();
-			sleep_bod_disable();
-			sei();
-			sleep_cpu();
-			sleep_disable();
-			sei();
-		} while (0);
-	}
-	ADCSRA |= _BV(ADEN); /* Re-enable ADC. */
-	wdt_int_sleep_mode = false;
-}
-
-static void wdt_enable_with_full_reset() {
-	wdt_enable(WDTO_8S);   /* Start watchdog timer for 8s. */
-	WDTCSR |= (1 << WDIE); /* Enable watchdog interrupt. */
-}
-
-static inline void disable_recording_interrupts() {
-	TIMSK1 &= ~(_BV(OCIE1A) | _BV(OCIE1B));
-}
-
 enum AdcChannel : uint8_t {
 	AdcChannel0    = 0,
 	AdcChannel1    = 1,
@@ -106,7 +56,6 @@ enum AdcChannel : uint8_t {
 	AdcChannelGnd  = 15,
 };
 
-EEPROM_Settings_Class settings;
 File file;
 #if defined(SAMPLE_MODE_U8)
 #define SAMPLE_BUF_SIZE 256
@@ -227,111 +176,23 @@ static void wav_write_header(uint32_t nsamples) {
 	}
 }
 
-void show_help() {
-	printf(F("Commands:\n"));
-	printf(F("  help                               --  Display this page.\n"));
-	printf(F("  exit                               --  Leave command mode.\n"));
-	printf(F("  get wait                           --  Display current delay setting.\n"));
-	printf(F("  set wait <number> [minutes|hours]  --  Change current delay setting.\n"));
-	printf(F("  set serial [on|off]                --  Write log to serial output.\n"));
-}
-
-void command_loop() {
-	// Process Commands
-	if (Serial.available()) {
-		char args[6][20];
-		size_t len = 0;
-		size_t n_args = 0;
-		int c = getchar();
-		while (c != '\n' && n_args < 4) {
-			if (c == ' ')
-				c = getchar();
-			else {
-				do {
-					args[n_args][len++] = c;
-					c = getchar();
-				} while (c != ' ' && c != '\n' && len < 20-1);
-				args[n_args][len] = 0;
-				len = 0;
-				n_args++;
-			}
-		}
-		if (n_args >= 1) {
-			if (fstreq(args[0], F("set"))) {
-				if ((n_args == 3 || n_args == 4) && fstreq(args[1], F("wait"))) {
-					float n = atof(args[2]);
-					unsigned long mins;
-					if (n_args == 4 && (fstreq(args[3], F("hours")) || fstreq(args[3], F("hour"))))
-						mins = 60.f * n;
-					else
-						mins = n;
-					settings.recording_delay = mins;
-					settings.save();
-					printf(F("Set waiting time to %lu minutes or "), settings.recording_delay);
-					print_special((float)settings.recording_delay / 60.f);
-					printf(F(" hours.\n"));
-				} else if (n_args == 3 && fstreq(args[1], F("serial"))) {
-					if (fstreq(args[2], F("on"))) {
-						settings.serial_log = true;
-						settings.save();
-						printf(F("Serial log enabled.\n"));
-					} else if (fstreq(args[2], F("off"))) {
-						settings.serial_log = false;
-						settings.save();
-						printf(F("Serial log disabled.\n"));
-					} else {
-						printf(F("Usage: 'set serial [on|off]'.\n"));
-					}
-				} else {
-					printf(F("Invalid usage of 'set'.\n"));
-					show_help();
-				}
-			} else if (fstreq(args[0], F("get"))) {
-				if (n_args == 2 && fstreq(args[1], F("wait"))) {
-					printf(F("Current waiting time: %lu minutes or "), settings.recording_delay);
-					print_special((float)settings.recording_delay / 60.f);
-					printf(F(" hours.\n"));
-				} else {
-					printf(F("Invalid usage of 'get'.\n"));
-					show_help();
-				}
-			} else if (fstreq(args[0], F("help"))) {
-				show_help();
-			} else if (fstreq(args[0], F("exit"))) {
-				printf(F("Bye!\n"));
-				Serial.flush();
-				full_reset();
-			} else
-				printf(F("Invalid command: '%s'. Type 'help' for a list of commands.\n"), args[0]);
-		} else {
-			printf(F("Please specify a command. Type 'help' for a list of commands.\n"));
-		}
-	}
-}
-
 void setup() {
 	// Serial Setup
 	Serial.begin(9600); /* Set baud rate. */
 	io_setup(); /* Add printf support. */
+	// Component Switch Setup
+#ifdef PIN_COMPONENT_SWITCH
+	pinMode(PIN_COMPONENT_SWITCH, OUTPUT);
+#endif
 	// Load EEPROM Data
 	settings.load();
 	// Handle Commands
 	info(F("Type anything in the next 4s to enter command mode.\n"));
 	for (size_t i = 0; i < 4 * 4; i++) {
-		if (Serial.available()) {
-			printf(F("You are now in command mode. Reset to exit. Type 'help' for a list of commands.\n"));
-			while (Serial.available()) Serial.read();
-			while (1) {
-				command_loop();
-				delay(50);
-			}
-		}
+		if (Serial.available())
+			cmd();
 		delay(250);
 	}
-	// Component Switch Setup
-#ifdef PIN_COMPONENT_SWITCH
-	pinMode(PIN_COMPONENT_SWITCH, OUTPUT);
-#endif
 	// Delayed Triggering
 	if (settings.recording_delay) {
 #ifdef PIN_COMPONENT_SWITCH
@@ -360,7 +221,7 @@ void setup() {
 	char filename[32];
 	do {
 		filenum++;
-		snprintf(filename, 32, "rec_%03u.wav", filenum);
+		snprintf(filename, 32, REC_FILE_FMT, filenum);
 	} while (SD.exists(filename));
 	// Open File
 	file = SD.open(filename, O_READ | O_WRITE | O_CREAT); /* Seeking doesn't seem to work with FILE_WRITE?! */
diff --git a/spybug/sys.cpp b/spybug/sys.cpp
new file mode 100644
index 0000000..fb31e04
--- /dev/null
+++ b/spybug/sys.cpp
@@ -0,0 +1,35 @@
+// Copyright 2022 Darwin Schuppan <darwin@nobrain.org>
+// SPDX license identifier: MIT
+
+#include "sys.hh"
+
+static volatile bool wdt_int_sleep_mode = false;
+ISR (WDT_vect) {
+	if (wdt_int_sleep_mode)
+		wdt_disable();
+	else
+		full_reset();
+}
+
+/* Based on https://github.com/rocketscream/Low-Power. */
+void low_power_sleep_minutes(unsigned long t) {
+	wdt_int_sleep_mode = true;
+	ADCSRA &= ~_BV(ADEN); /* Disable ADC. */
+	for (unsigned long i = 0; 8ul * i < 60ul * t; i++) {
+		// Power Down for 8s
+		wdt_enable(WDTO_8S);   /* Start watchdog timer for 8s. */
+		WDTCSR |= (1 << WDIE); /* Enable watchdog interrupt. */
+		do {
+			set_sleep_mode(SLEEP_MODE_PWR_DOWN);
+			cli();
+			sleep_enable();
+			sleep_bod_disable();
+			sei();
+			sleep_cpu();
+			sleep_disable();
+			sei();
+		} while (0);
+	}
+	ADCSRA |= _BV(ADEN); /* Re-enable ADC. */
+	wdt_int_sleep_mode = false;
+}
diff --git a/spybug/sys.hh b/spybug/sys.hh
new file mode 100644
index 0000000..d89742f
--- /dev/null
+++ b/spybug/sys.hh
@@ -0,0 +1,22 @@
+// Copyright 2022 Darwin Schuppan <darwin@nobrain.org>
+// SPDX license identifier: MIT
+
+#pragma once
+
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <avr/wdt.h>
+#include <avr/sleep.h>
+
+static void (*full_reset)() = nullptr;
+
+void low_power_sleep_minutes(unsigned long t);
+
+static inline void wdt_enable_with_full_reset() {
+	wdt_enable(WDTO_8S);   /* Start watchdog timer for 8s. */
+	WDTCSR |= (1 << WDIE); /* Enable watchdog interrupt. */
+}
+
+static inline void disable_recording_interrupts() {
+	TIMSK1 &= ~(_BV(OCIE1A) | _BV(OCIE1B));
+}