diff --git a/FCCee/IDEA/compact/IDEA_o2_v01/DREndcapTubes_o1_v01.xml b/FCCee/IDEA/compact/IDEA_o2_v01/DREndcapTubes_o1_v01.xml
index 10e4c2eba..78d485cf4 100644
--- a/FCCee/IDEA/compact/IDEA_o2_v01/DREndcapTubes_o1_v01.xml
+++ b/FCCee/IDEA/compact/IDEA_o2_v01/DREndcapTubes_o1_v01.xml
@@ -270,8 +270,21 @@
       <segmentation type="CartesianGridXY" 
              grid_size_x="1*mm" 
              grid_size_y="1*mm"/>
+      <!--
+          Volume ids of this subdetector are defined as "system" for the entire endcap calorimeter,
+	  "stave" for the phi-slices, "tower" for the towers (trapezoids) inside a phi-slice,
+	  "air" dummy for the moment but useful if a tower supporting structure will be added,
+	  "col" and "row" colum and row of tube inside a tower, "clad" "core" "cherenkov"
+	  cladding core volumes and cherenkov identifiers of an optical fiber
+      -->
+      <!--
+	  This subdetector is supposed to be used with regexSD, therefore volumeID(aStep) will
+	  not work in the DRTubesSDAction to retrieve the volumeID. Instead we use g4 copynumbers
+	  accessed from the G4Step to recreate the 64-bit volume ID inside DRTubesSDAction.
+	  Do not change these ids, contact the experts (Lorenzo Pezzotti) before any modification.
+      -->
       <!-- NO SPACES BETWEEN ID DESCRIPTORS!!! -->
-      <id>stave:10,tower:6,air:1,col:16,row:16,clad:1,core:1,cherenkov:1</id>
+      <id>system:5,stave:10,tower:6,air:1,col:16,row:16,clad:1,core:1,cherenkov:1</id>
     </readout>
   </readouts> 
 
diff --git a/FCCee/IDEA/compact/IDEA_o2_v01/DectDimensions_IDEA_o2_v01.xml b/FCCee/IDEA/compact/IDEA_o2_v01/DectDimensions_IDEA_o2_v01.xml
index 9895c63b1..d8e9a9470 100644
--- a/FCCee/IDEA/compact/IDEA_o2_v01/DectDimensions_IDEA_o2_v01.xml
+++ b/FCCee/IDEA/compact/IDEA_o2_v01/DectDimensions_IDEA_o2_v01.xml
@@ -53,6 +53,11 @@
 
 
     <!-- Dual-Readout Endcap Tubes (DRET) calorimeter DetID-->
+    <!-- This number is used in DRTubesSDAction to recreate
+	 the volume ids for this subdetector.
+	 Do not change it, contact the experts (Lorenzo Pezzoti)
+	 before any modification.
+    -->
     <constant name="DetID_DREndcapTubes"          value=" 25"/>
 
     <constant name="DetID_muonSystem"       value=" 26"/>
diff --git a/detector/calorimeter/dual-readout-tubes/src/DREndcapTubes_o1_v01.cpp b/detector/calorimeter/dual-readout-tubes/src/DREndcapTubes_o1_v01.cpp
index 3f2ae408c..a9061e6fd 100644
--- a/detector/calorimeter/dual-readout-tubes/src/DREndcapTubes_o1_v01.cpp
+++ b/detector/calorimeter/dual-readout-tubes/src/DREndcapTubes_o1_v01.cpp
@@ -511,6 +511,7 @@ static Ref_t create_detector(Detector& description, xml_h e, SensitiveDetector s
   Volume motherVolume = description.pickMotherVolume(sdet);
   // Place the assembly container inside the mother volume
   PlacedVolume AssemblyEndcapPV = motherVolume.placeVolume(AssemblyEndcap);
+  AssemblyEndcapPV.addPhysVolID("system",x_det.id());
   sdet.setPlacement(AssemblyEndcapPV);
 
   std::cout << "--> DREndcapTubes::create_detector() end" << std::endl;
diff --git a/plugins/DRTubesSDAction.cpp b/plugins/DRTubesSDAction.cpp
index 6f06a3206..483846579 100644
--- a/plugins/DRTubesSDAction.cpp
+++ b/plugins/DRTubesSDAction.cpp
@@ -155,7 +155,8 @@ bool Geant4SensitiveAction<DRTubesSDData>::process(const G4Step* aStep,
   auto StaveID = static_cast<unsigned int>(aStep->GetPreStepPoint()->GetTouchable()->GetCopyNumber(4));
 
   VolumeID VolID = 0; // recreate the 64-bit VolumeID
-  BitFieldCoder bc("stave:10,tower:6,air:1,col:16,row:16,clad:1,core:1,cherenkov:1");
+  BitFieldCoder bc("system:5,stave:10,tower:6,air:1,col:16,row:16,clad:1,core:1,cherenkov:1");
+  bc.set(VolID, "system", 25); // this number is set in DectDimensions_IDEA_o2_v01.xml
   bc.set(VolID, "stave" , StaveID);
   bc.set(VolID, "tower" , TowerID);
   bc.set(VolID, "air", 0);
@@ -178,8 +179,6 @@ bool Geant4SensitiveAction<DRTubesSDData>::process(const G4Step* aStep,
 
   if (IsScin) {  // it is a scintillating fiber
 
-    //m_userData.fEvtAction->AddEdepScin(Edep);
-
     if (aStep->GetTrack()->GetDefinition()->GetPDGCharge() == 0 || steplength == 0.) {
       return true;  // not ionizing particle
     }
@@ -188,12 +187,9 @@ bool Geant4SensitiveAction<DRTubesSDData>::process(const G4Step* aStep,
       DRTubesSglHpr::SmearSSignal(DRTubesSglHpr::ApplyBirks(Edep, steplength));
     signalhit = DRTubesSglHpr::AttenuateSSignal(signalhit, distance_to_sipm);
     if (signalhit == 0) return true;
-    //m_userData.fEvtAction->AddSglScin(signalhit);
   }  // end of scintillating fibre sigal calculation
 
   else {  // it is a Cherenkov fiber
-    // save mc truth info in analysismanager auxiliary outputfile
-    //m_userData.fEvtAction->AddEdepCher(Edep);
     // calculate the signal in terms of Cherenkov photo-electrons
     if (aStep->GetTrack()->GetParticleDefinition() == G4OpticalPhoton::Definition()) {
       G4OpBoundaryProcessStatus theStatus = Undefined;
@@ -221,8 +217,6 @@ bool Geant4SensitiveAction<DRTubesSDData>::process(const G4Step* aStep,
           G4int c_signal = DRTubesSglHpr::SmearCSignal();
           signalhit = DRTubesSglHpr::AttenuateCSignal(c_signal, distance_to_sipm);
           if (signalhit == 0) return true;
-          // save mc truth info in analysismanager auxiliary outputfile
-          //m_userData.fEvtAction->AddSglCher(signalhit);
           aStep->GetTrack()->SetTrackStatus(fStopAndKill);
           break;
         }