diff --git a/README.md b/README.md
index 8833522..ba8adc2 100644
--- a/README.md
+++ b/README.md
@@ -203,7 +203,8 @@ Il contient l'ID de la figurine sur les bits 0-5 de l'octet, si la figurine
 est un personnage (1) ou une année (0) sur le bit 6 et si la figurine a été posée
 (0) ou retirée (1) sur le bit 7.  
 Ainsi, si on interprète l'octet comme un nombre signé, si le nombre est négatif
-on sait que la figurine a été retirée.
+on sait que la figurine a été retirée.  
+**_Dû à un détail d'implémentation, l'identifiant 127 est invalide et réservé._**
 
 #### Schéma
 ```
diff --git a/include/RFID.h b/include/RFID.h
index 66a42f8..1c8bd8b 100644
--- a/include/RFID.h
+++ b/include/RFID.h
@@ -32,6 +32,8 @@ struct uidNode {
 class RFID {
 public:
 	static constexpr int maxTags = 2;
+	/* Error value returned when checking for new or gone tags. */
+	static constexpr int8_t checkFail = -1;
 
 	/***
 	 * Use the main SPI port and NFC chip select by default, but allow choosing
@@ -48,7 +50,8 @@ public:
 	 * at a time, another call would be needed to get eventual concurrent events.
 	 * This updates the respective lists and returns the ID with the direction
 	 * of the change.
-	 * @return 0 if no change, ID if new tag detected, ID & sign bit if the tag left.
+	 * @return ID if new tag detected, ID & sign bit if the tag left
+	 * @return RFID::checkFail if no change or error.
 	 */
 	int8_t checkTags();
 
diff --git a/src/RFID.cpp b/src/RFID.cpp
index 2b15851..62a4a2f 100644
--- a/src/RFID.cpp
+++ b/src/RFID.cpp
@@ -52,21 +52,21 @@ int8_t RFID::checkTags() {
 	if ( currentActiveTags >= maxTags ||
 		 !mfrc.PICC_IsNewCardPresent() ||
 		 !mfrc.PICC_ReadCardSerial()) {
-		return 0;
+		return checkFail;
 	}
 
 	// Assume we have a new tag.
 	uidNode* newTag = addActiveTag(mfrc.uid);
 	// Tag ID is put in a specific block, which can be read after from comData.
 	if ( !newTag ) {
-		return 0;
+		return checkFail;
 	}
 	// If the read fails, we cannot use this tag anyway so remove it from the list.
 	if (!readBlock(newTag->uid, tagIdBlock) ) {
 		removeActiveTag(newTag, nullptr);
-		return 0;
+		return checkFail;
 	}
-	// Don' t check the ID, otherwise we cannot program the tag.
+	// Don't check the ID, otherwise we cannot program the tag.
 	newTag->tag_ID = comData[0];
 	return newTag->tag_ID;
 }
diff --git a/src/main.cpp b/src/main.cpp
index b281973..dcaf1c7 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -67,7 +67,7 @@ __attribute__((noreturn)) int main() {
 		speaker.checkPlayingAndDisable();
 
 		tagEvent = rfid.checkTags();
-		if (tagEvent) {
+		if (tagEvent != RFID::checkFail) {
 			Com::sendFigUpdate(tagEvent);
 			/* Currently, we only play effects when placing a new figurine. */
 			if (!isIdGone(tagEvent)) {