diff --git a/app/client/alarm.js b/app/client/alarm.js
index 97a1a0a..16a1d12 100644
--- a/app/client/alarm.js
+++ b/app/client/alarm.js
@@ -36,7 +36,9 @@ Template.alarm.helpers({
     var temperatures = last_sensor_reading().temperatures;
 
     for (var i in temperatures) {
-      result += '' + parseFloat(temperatures[i]).toFixed(1) + ' °C ';
+      var temperature = parseFloat(temperatures[i]).toFixed(1);
+      var temperatureLabel = (Meteor.zoblak.shared.valid_temperature(temperature)) ? temperature : "XX.X";
+      result += '' + temperatureLabel + ' °C ';
     }
     return result;
   },
diff --git a/app/lib/zoblak.js b/app/lib/zoblak.js
index 700d55a..07397aa 100644
--- a/app/lib/zoblak.js
+++ b/app/lib/zoblak.js
@@ -27,6 +27,12 @@ Meteor.zoblak.client = {
   }
 }
 
+Meteor.zoblak.shared = {
+  valid_temperature: function(value) {
+      return (parseFloat(value) > -40 && parseFloat(value) < 50);
+  }
+}
+
 Meteor.zoblak.server = {
   controller_state: function(controller_id) {
     var result = {}
diff --git a/app/server/methods.js b/app/server/methods.js
index 7171cb1..c4e8d8b 100644
--- a/app/server/methods.js
+++ b/app/server/methods.js
@@ -158,7 +158,7 @@ function saveAlarmSettings(controller_id, minTemperature, maxTemperature, timeou
       'config.sms4': smsNumbers[3]
     }
   });
-  
+
   var jobName = "automatic_alarm_" + controller_id;
 
   SyncedCron.remove(jobName);
@@ -186,6 +186,7 @@ reactToAlarmData = function(controller_id) {
   var state = Meteor.zoblak.server.controller_state(controller_id);
   var config = state.config;
 
+
   var minTemperature = function(temperatures) {
     // if it gets a lot colder than absolute zero
     // we will have more problems than the bug in this code
@@ -197,7 +198,7 @@ reactToAlarmData = function(controller_id) {
       }
     }
     return minimal;
-  }
+  };
 
   var maxTemperature = function(temperatures) {
     // obviously - hell is not supported in this version
@@ -209,11 +210,13 @@ reactToAlarmData = function(controller_id) {
       }
     }
     return maximal;
-  }
+  };
 
-  var tooCold = config.minTemperature && (minTemperature(reading.temperatures) < config.minTemperature);
+  var temperatures = (reading.temperatures || []).filter(Meteor.zoblak.shared.valid_temperature);
 
-  var tooHot = config.maxTemperature && (maxTemperature(reading.temperatures) > config.maxTemperature);
+  var tooCold = config.minTemperature && (minTemperature(temperatures) < config.minTemperature);
+
+  var tooHot = config.maxTemperature && (maxTemperature(temperatures) > config.maxTemperature);
 
   var minutesSinceLastBoxContact = reading.lastBoxContact ? moment(new Date()).diff(moment(reading.lastBoxContact), 'minutes') : -1;
   var boxSilent = config.timeoutBox && minutesSinceLastBoxContact > config.timeoutBox;