diff --git a/src/cmdline.cc b/src/cmdline.cc
index 29c48b1..349b75d 100644
--- a/src/cmdline.cc
+++ b/src/cmdline.cc
@@ -360,7 +360,7 @@ unique_ptr<Configuration> parseCommandLine(int argc, char **argv) {
 
         if (mt == MeterType::UNKNOWN) error("Not a valid meter type \"%s\"\n", type.c_str());
         if (!isValidMatchExpressions(id, true)) error("Not a valid id nor a valid meter match expression \"%s\"\n", id.c_str());
-        if (!isValidKey(key)) error("Not a valid meter key \"%s\"\n", key.c_str());
+        if (!isValidKey(key, mt)) error("Not a valid meter key \"%s\"\n", key.c_str());
         vector<string> no_meter_shells, no_meter_jsons;
         c->meters.push_back(MeterInfo(name, type, id, key, modes, no_meter_shells, no_meter_jsons));
     }
diff --git a/src/config.cc b/src/config.cc
index f7cb8f6..4f5f52c 100644
--- a/src/config.cc
+++ b/src/config.cc
@@ -128,7 +128,7 @@ void parseMeterConfig(Configuration *c, vector<char> &buf, string file)
         warning("Not a valid meter id nor a valid meter match expression \"%s\"\n", id.c_str());
         use = false;
     }
-    if (!isValidKey(key)) {
+    if (!isValidKey(key, mt)) {
         warning("Not a valid meter key \"%s\"\n", key.c_str());
         use = false;
     }
diff --git a/src/meter_izar.cc b/src/meter_izar.cc
index 67e98c7..16ba4c3 100644
--- a/src/meter_izar.cc
+++ b/src/meter_izar.cc
@@ -38,10 +38,13 @@ private:
 
     void processContent(Telegram *t);
     uint32_t convertKey(const char *hex);
+    uint32_t convertKey(const vector<uchar> &bytes);
     uint32_t uint32FromBytes(const vector<uchar> &data, int offset, bool reverse = false);
     vector<uchar> decodePrios(const vector<uchar> &payload, uint32_t key);
 
     double total_water_consumption_l_ {};
+
+    vector<uint32_t> keys;
 };
 
 unique_ptr<WaterMeter> createIzar(WMBus *bus, MeterInfo &mi)
@@ -52,6 +55,16 @@ unique_ptr<WaterMeter> createIzar(WMBus *bus, MeterInfo &mi)
 MeterIzar::MeterIzar(WMBus *bus, MeterInfo &mi) :
     MeterCommonImplementation(bus, mi, MeterType::IZAR, MANUFACTURER_SAP)
 {
+    if (!key().empty())
+        keys.push_back(convertKey(key()));
+
+    // fallback to default keys if no custom key provided
+    if (keys.empty())
+    {
+        keys.push_back(convertKey(PRIOS_DEFAULT_KEY1));
+        keys.push_back(convertKey(PRIOS_DEFAULT_KEY2));
+    }
+
     addMedia(0x01); // Oil meter? why?
 
     addLinkMode(LinkMode::T1);
@@ -96,6 +109,11 @@ uint32_t MeterIzar::convertKey(const char *hex)
 {
     vector<uchar> bytes;
     hex2bin(hex, &bytes);
+    return convertKey(bytes);
+}
+
+uint32_t MeterIzar::convertKey(const vector<uchar> &bytes)
+{
     uint32_t key1 = uint32FromBytes(bytes, 0);
     uint32_t key2 = uint32FromBytes(bytes, 4);
     uint32_t key = key1 ^ key2;
@@ -109,10 +127,6 @@ void MeterIzar::processContent(Telegram *t)
     frame.insert(frame.end(), t->parsed.begin(), t->parsed.end());
     frame.insert(frame.end(), t->payload.begin(), t->payload.end());
 
-    vector<uint32_t> keys;
-    keys.push_back(convertKey(PRIOS_DEFAULT_KEY1));
-    keys.push_back(convertKey(PRIOS_DEFAULT_KEY2));
-
     vector<uchar> decoded_content;
     for (auto& key : keys) {
         decoded_content = decodePrios(frame, key);
diff --git a/src/util.cc b/src/util.cc
index 27ba4f2..37a2f0a 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -16,6 +16,7 @@
 */
 
 #include"util.h"
+#include"meters.h"
 #include<dirent.h>
 #include<functional>
 #include<grp.h>
@@ -530,10 +531,11 @@ bool doesIdMatchExpressions(string& id, vector<string>& mes)
     return false;
 }
 
-bool isValidKey(string& key)
+bool isValidKey(string& key, MeterType mt)
 {
     if (key.length() == 0) return true;
-    if (key.length() != 32) return false;
+    if ((mt == MeterType::IZAR && key.length() != 16) ||
+        (mt != MeterType::IZAR && key.length() != 32)) return false;
     vector<uchar> tmp;
     return hex2bin(key, &tmp);
 }
diff --git a/src/util.h b/src/util.h
index cd2542b..6a68dc7 100644
--- a/src/util.h
+++ b/src/util.h
@@ -24,6 +24,8 @@
 #include<functional>
 #include<vector>
 
+enum class MeterType;
+
 void onExit(std::function<void()> cb);
 void restoreSignalHandlers();
 bool gotHupped();
@@ -75,7 +77,7 @@ bool isValidMatchExpressions(std::string ids, bool non_compliant);
 bool doesIdMatchExpression(std::string id, std::string match);
 bool doesIdMatchExpressions(std::string& id, std::vector<std::string>& ids);
 
-bool isValidKey(std::string& key);
+bool isValidKey(std::string& key, MeterType mt);
 bool isFrequency(std::string& fq);
 bool isNumber(std::string& fq);