diff --git a/ampel-firmware/co2_sensor.cpp b/ampel-firmware/co2_sensor.cpp
index 2c8ea456395d19ede00bc1c938893f66691517ca..f58e63f278570b82e874949e61653d6336c1d3fe 100644
--- a/ampel-firmware/co2_sensor.cpp
+++ b/ampel-firmware/co2_sensor.cpp
@@ -17,6 +17,7 @@ namespace config {
   const bool debug_sensor_states = false; // If true, log state transitions over serial console
 }
 
+//WARNING: Be very careful when connecting S8 to +5V and GND. There's no protection if polarity is reversed, and S8 would break.
 #if defined(ESP8266)
 //NOTE: This library requires much less memory than SoftwareSerial.h
 #  include "src/lib/Esp8266EdgeSoftwareSerial/ESP8266SoftwareSerial.h"