diff --git a/firmware/firmware.ino b/firmware/firmware.ino
index 9008d5b..f6b9201 100644
--- a/firmware/firmware.ino
+++ b/firmware/firmware.ino
@@ -47,7 +47,7 @@
 //*************************************************************************//
 
 const uint8_t VALUES = 8;
-float currentSensorData[VALUES] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
+float currentSensorData[VALUES] = {nanf("no value"), nanf("no value"), nanf("no value"), nanf("no value"), nanf("no value"), nanf("no value"), nanf("no value"), nanf("no value")};
 float (*sensors[VALUES])() = {};
 
 uint16_t update_sensor_cnt      = 0;
@@ -233,7 +233,7 @@ void _loop() {
     if (sensors[i]) {
       currentSensorData[i] = sensors[i]();
     } else {
-      currentSensorData[i] = 0xFFFFFFFF;
+      currentSensorData[i] = nan("no value");
     }
   }
 
diff --git a/firmware/sensor_battery.ino b/firmware/sensor_battery.ino
index 1a19a74..593be35 100644
--- a/firmware/sensor_battery.ino
+++ b/firmware/sensor_battery.ino
@@ -1,4 +1,4 @@
-float _sensor_battery_saveMode = 0;
+float _sensor_battery_saveMode = nan("no battery");
 uint16_t energySavingIterations = 0;
 
 // Copied from https://arduinodiy.wordpress.com/2016/12/25/monitoring-lipo-battery-voltage-with-wemos-d1-minibattery-shield-and-thingspeak/