diff --git a/Simulation/DetSimSD/include/DetSimSD/CaloSensitiveDetector.h b/Simulation/DetSimSD/include/DetSimSD/CaloSensitiveDetector.h
index 5e228698bcaeab116263d4ebf1c19cb0341b5800..0ad3398ae7592136d63c682ba3a1d1f5efdbf487 100644
--- a/Simulation/DetSimSD/include/DetSimSD/CaloSensitiveDetector.h
+++ b/Simulation/DetSimSD/include/DetSimSD/CaloSensitiveDetector.h
@@ -15,7 +15,7 @@ public:
     typedef G4THitsCollection<CalorimeterHit> CaloHitCollection;
 
 public:
-    CaloSensitiveDetector(const std::string& name, dd4hep::Detector& description);
+    CaloSensitiveDetector(const std::string& name, dd4hep::Detector& description, bool unmerge=true);
 
 public:
     // Geant4 interface
@@ -31,6 +31,7 @@ protected:
 
     HitCollection* m_hc;
     std::map<unsigned long, CalorimeterHit*> m_hitMap;
+    bool                                     m_unmerge;
 };
 
 
diff --git a/Simulation/DetSimSD/src/CaloSensitiveDetector.cpp b/Simulation/DetSimSD/src/CaloSensitiveDetector.cpp
index 25ce6e6e135f3df08c067ba511267877c9419129..8fd0dcb7547e709e787987b34b5919d8bb95ee30 100644
--- a/Simulation/DetSimSD/src/CaloSensitiveDetector.cpp
+++ b/Simulation/DetSimSD/src/CaloSensitiveDetector.cpp
@@ -4,9 +4,10 @@
 
 #include <algorithm>
 
-CaloSensitiveDetector::CaloSensitiveDetector(const std::string& name, dd4hep::Detector& description)
+CaloSensitiveDetector::CaloSensitiveDetector(const std::string& name, dd4hep::Detector& description, bool unmerge)
     : DDG4SensitiveDetector(name, description),
-      m_hc(nullptr) {
+      m_hc(nullptr),
+      m_unmerge(unmerge){
     const std::string& coll_name = m_sensitive.hitsCollection();
     collectionName.insert(coll_name);
 }
@@ -38,7 +39,7 @@ CaloSensitiveDetector::ProcessHits(G4Step* step, G4TouchableHistory*) {
     unsigned long id = getCellID( step );
     //std::cout << name << " " << id << std::endl;
     CalorimeterHit* hit=nullptr;
-    if(name.find("Merge")==-1&&name.find("merge")==-1) find(m_hc,dd4hep::sim::HitPositionCompare<CalorimeterHit>(pos));
+    if(m_unmerge) hit=find(m_hc,dd4hep::sim::HitPositionCompare<CalorimeterHit>(pos));
     else{
       std::map<unsigned long, CalorimeterHit*>::iterator it = m_hitMap.find(id);
       if(it!=m_hitMap.end()) hit = it->second;
@@ -46,9 +47,9 @@ CaloSensitiveDetector::ProcessHits(G4Step* step, G4TouchableHistory*) {
     //    G4cout << "----------- Geant4GenericSD<Calorimeter>::buildHits : position : " << pos << G4endl;
     if ( !hit ) {
         hit = new CalorimeterHit(pos);
-        hit->cellID  = getCellID( step );
+        hit->cellID  = id; //getCellID( step );
         m_hc->insert(hit);
-	if(name.find("Merge")!=-1||name.find("merge")!=-1) m_hitMap[id] = hit;
+	if(!m_unmerge) m_hitMap[id] = hit;
     }
     hit->truth.push_back(contrib);
     hit->energyDeposit += contrib.deposit;
diff --git a/Simulation/DetSimSD/src/CalorimeterSensDetTool.cpp b/Simulation/DetSimSD/src/CalorimeterSensDetTool.cpp
index 844104e28b4fda57d60ab1100d38d7ae7d3c25b8..cb7be22964898405fc9d6d8c5cae0e66cf34d9ed 100644
--- a/Simulation/DetSimSD/src/CalorimeterSensDetTool.cpp
+++ b/Simulation/DetSimSD/src/CalorimeterSensDetTool.cpp
@@ -35,7 +35,15 @@ CalorimeterSensDetTool::createSD(const std::string& name) {
 
     dd4hep::Detector* dd4hep_geo = m_geosvc->lcdd();
 
-    G4VSensitiveDetector* sd = new CaloSensitiveDetector(name, *dd4hep_geo);
+    bool flagUnmerge = false;
+    for(auto cal_name : m_unmergeCals){
+      if(cal_name==name){
+	flagUnmerge = true;
+	break;
+      }
+    }
+    G4VSensitiveDetector* sd = new CaloSensitiveDetector(name, *dd4hep_geo, flagUnmerge);
+    debug() << name << " set to merge true/false = " << !flagUnmerge << endmsg;
 
     return sd;
 }
diff --git a/Simulation/DetSimSD/src/CalorimeterSensDetTool.h b/Simulation/DetSimSD/src/CalorimeterSensDetTool.h
index f3e0796b55670534b10cfb242093a577c724f4e9..dd1b24f078b605b1b0ee4c8cd67ddf87a9aa1784 100644
--- a/Simulation/DetSimSD/src/CalorimeterSensDetTool.h
+++ b/Simulation/DetSimSD/src/CalorimeterSensDetTool.h
@@ -29,6 +29,7 @@ private:
     // in order to initialize SD, we need to get the lcdd()
     SmartIF<IGeomSvc> m_geosvc;
 
+    Gaudi::Property<std::vector<std::string> > m_unmergeCals{this, "UnmergedCalNames", {}};
 };
 
 #endif