diff --git a/apps/secs_server.cpp b/apps/secs_server.cpp
index b884397..23d8a3f 100644
--- a/apps/secs_server.cpp
+++ b/apps/secs_server.cpp
@@ -17,6 +17,7 @@
 #include "secsgem/gem/control_state.hpp"
 #include "secsgem/gem/data_model.hpp"
 #include "secsgem/gem/e116_constants.hpp"
+#include "secsgem/gem/e157_constants.hpp"
 #include "secsgem/gem/e90_constants.hpp"
 #include "secsgem/gem/messages.hpp"
 #include "secsgem/gem/router.hpp"
@@ -365,6 +366,32 @@ int main(int argc, char** argv) {
         }
       });
 
+  // ---- E157 module state-change emitter --------------------------------
+  // Every module transition fires the generic ModuleProcessStateChange
+  // CEID plus the state-specific one, mirroring secsgem-py's per-module
+  // CEID granularity.  Hosts that don't subscribe to the specific CEID
+  // can still listen on the generic one to drive an internal FSM.
+  model->modules.set_state_change_handler(
+      [logfn, emit_event](const std::string& mod, gem::ModuleState from,
+                          gem::ModuleState to, gem::ModuleEvent ev) {
+        logfn(std::string("MOD ") + mod + ": " +
+              gem::module_state_name(from) + " -> " +
+              gem::module_state_name(to) + "  (" +
+              gem::module_event_name(ev) + ")");
+        emit_event(gem::e157::kCeidModuleProcessStateChange);
+        switch (to) {
+          case gem::ModuleState::NotExecuting:
+            emit_event(gem::e157::kCeidModuleNotExecuting); break;
+          case gem::ModuleState::GeneralExecuting:
+            emit_event(gem::e157::kCeidModuleGeneralExecuting); break;
+          case gem::ModuleState::StepExecuting:
+            emit_event(gem::e157::kCeidModuleStepExecuting); break;
+          case gem::ModuleState::StepCompleted:
+            emit_event(gem::e157::kCeidModuleStepCompleted); break;
+          case gem::ModuleState::NoState: break;
+        }
+      });
+
   // ---- Build the SECS dispatch table once -------------------------------
   gem::Router router;
 
diff --git a/include/secsgem/gem/e157_constants.hpp b/include/secsgem/gem/e157_constants.hpp
new file mode 100644
index 0000000..01681c2
--- /dev/null
+++ b/include/secsgem/gem/e157_constants.hpp
@@ -0,0 +1,16 @@
+#pragma once
+
+#include <cstdint>
+
+// E157 §6 standard collection-event identifiers, one per module state.
+// Equipment fires the matching CEID when a module transitions; hosts
+// subscribe via the standard S2F33 / S2F35 / S2F37 path.
+namespace secsgem::gem::e157 {
+
+inline constexpr uint32_t kCeidModuleProcessStateChange = 1570;
+inline constexpr uint32_t kCeidModuleNotExecuting       = 1571;
+inline constexpr uint32_t kCeidModuleGeneralExecuting   = 1572;
+inline constexpr uint32_t kCeidModuleStepExecuting      = 1573;
+inline constexpr uint32_t kCeidModuleStepCompleted      = 1574;
+
+}  // namespace secsgem::gem::e157