diff --git a/firmware/firmware.ino b/firmware/firmware.ino
index ac2b66a..8112c1a 100644
--- a/firmware/firmware.ino
+++ b/firmware/firmware.ino
@@ -18,6 +18,8 @@ char cardBuffer[CARD_BUFFER_LENGTH];
 
 #define CARD_DATA_LENGTH 10
 #define CARD_CHECK_LENGTH 2
+#define CARD_HEAD_BYTE 0x2
+#define CARD_TAIL_BYTE 0x3
 typedef struct __attribute__((packed)) cardData {
 	char head;
 	char data[CARD_DATA_LENGTH];
@@ -48,6 +50,7 @@ typedef struct __attribute__((packed)) cardData {
 #define LED_ERROR_BLINK_TIME 50
 
 #define EEPROM_SIZE 4095
+#define EEPROM_END_MARKER '$'
 
 enum wifiStates
 {
@@ -117,7 +120,7 @@ void tickerLoop()
 
 			if (readChar == -1) {
 				break;
-			} else if (readChar == 0x2) {
+			} else if (readChar == CARD_HEAD_BYTE) {
 				bufPos = 0;
 			}
 
@@ -127,7 +130,7 @@ void tickerLoop()
 
 			cardBuffer[bufPos++] = readChar;
 
-			if (readChar == 0x3 && bufPos == CARD_BUFFER_LENGTH) {
+			if (readChar == CARD_TAIL_BYTE && bufPos == CARD_BUFFER_LENGTH) {
 				if (lockState == LOCK_OFF && LEDState == LED_OFF) checkCard();
 				break;
 			}
@@ -177,7 +180,10 @@ void checkCard()
 {
 	cardData_t *cardData = (cardData_t *) cardBuffer;
 
-	if (cardData->head == 0x2 && cardData->tail == 0x3 && checksum(cardData)) {
+	if (cardData->head == CARD_HEAD_BYTE &&
+			cardData->tail == CARD_TAIL_BYTE &&
+			checksum(cardData)) {
+
 		String cardStr = String();
 		String authorizedCards = String();
 
@@ -188,7 +194,7 @@ void checkCard()
 		for (uint16_t i = 0; i < EEPROM_SIZE; i++) {
 			char tmp = EEPROM.read(i);
 			authorizedCards += tmp;
-			if (tmp == '$') break;
+			if (tmp == EEPROM_END_MARKER) break;
 		}
 
 		if (LOGGING) Serial.println("[INFO] Good scan from card: " + cardStr);
@@ -457,7 +463,7 @@ void getCards()
 		if (cardHTTPCode == HTTP_CODE_OK) {
 			if (LOGGING) Serial.print("[INFO] Resource found, parsing response: ");
 			String cardPayload = cardHTTP.getString();
-			cardPayload += "$"; // Mark the end
+			cardPayload += String(EEPROM_END_MARKER);
 			if (LOGGING) Serial.println(cardPayload);
 
 			noInterrupts(); // commit() disables interrupts, but we want an atomic EEPROM buffer write