diff --git a/EXRAIL2.cpp b/EXRAIL2.cpp
index ef4387c..77a090c 100644
--- a/EXRAIL2.cpp
+++ b/EXRAIL2.cpp
@@ -54,6 +54,7 @@
 #include "TrackManager.h"
 #include "Turntables.h"
 #include "IODevice.h"
+#include "EXRAILSensor.h"
 
 
 // One instance of RMFT clas is used for each "thread" in the automation.
@@ -251,6 +252,12 @@ if (compileFeatures & FEATURE_SIGNAL) {
       break;
     }
 
+    case OPCODE_ONSENSOR:
+        new EXRAILSensor(operand,progCounter+3,true );
+        break;
+    case OPCODE_ONBUTTON:
+        new EXRAILSensor(operand,progCounter+3,false );
+        break;
     case OPCODE_TURNOUT: {
       VPIN id=operand;
       int addr=getOperand(progCounter,1);
@@ -480,6 +487,7 @@ bool RMFT2::skipIfBlock() {
 }
 
 void RMFT2::loop() {
+  EXRAILSensor::checkAll();
 
   // Round Robin call to a RMFT task each time
   if (loopTask==NULL) return;
@@ -1084,6 +1092,8 @@ void RMFT2::loop2() {
   case OPCODE_ONGREEN:
   case OPCODE_ONCHANGE:
   case OPCODE_ONTIME:
+  case OPCODE_ONBUTTON:
+  case OPCODE_ONSENSOR:
 #ifndef IO_NO_HAL
   case OPCODE_DCCTURNTABLE: // Turntable definition ignored at runtime
   case OPCODE_EXTTTURNTABLE:  // Turntable definition ignored at runtime
diff --git a/EXRAIL2.h b/EXRAIL2.h
index 7075f26..1042d53 100644
--- a/EXRAIL2.h
+++ b/EXRAIL2.h
@@ -73,7 +73,7 @@ enum OPCODE : byte {OPCODE_THROW,OPCODE_CLOSE,OPCODE_TOGGLE_TURNOUT,
              OPCODE_ROUTE_ACTIVE,OPCODE_ROUTE_INACTIVE,OPCODE_ROUTE_HIDDEN,
              OPCODE_ROUTE_DISABLED,
              OPCODE_STASH,OPCODE_CLEAR_STASH,OPCODE_CLEAR_ALL_STASH,OPCODE_PICKUP_STASH,
-
+             OPCODE_ONBUTTON,OPCODE_ONSENSOR,
              // OPcodes below this point are skip-nesting IF operations
              // placed here so that they may be skipped as a group
              // see skipIfBlock()
diff --git a/EXRAIL2MacroReset.h b/EXRAIL2MacroReset.h
index ce242ea..c799ddf 100644
--- a/EXRAIL2MacroReset.h
+++ b/EXRAIL2MacroReset.h
@@ -114,6 +114,8 @@
 #undef ONGREEN
 #undef ONRED
 #undef ONROTATE
+#undef ONBUTTON
+#undef ONSENSOR
 #undef ONTHROW 
 #undef ONCHANGE
 #undef PARSE
@@ -279,6 +281,8 @@
 #define ONROTATE(turntable_id)
 #define ONTHROW(turnout_id) 
 #define ONCHANGE(sensor_id)
+#define ONSENSOR(sensor_id)
+#define ONBUTTON(sensor_id)
 #define PAUSE
 #define PIN_TURNOUT(id,pin,description...) 
 #define PRINT(msg) 
diff --git a/EXRAILMacros.h b/EXRAILMacros.h
index 7db52dc..508540a 100644
--- a/EXRAILMacros.h
+++ b/EXRAILMacros.h
@@ -553,6 +553,8 @@ int RMFT2::onLCCLookup[RMFT2::countLCCLookup];
 #endif
 #define ONTHROW(turnout_id) OPCODE_ONTHROW,V(turnout_id),
 #define ONCHANGE(sensor_id) OPCODE_ONCHANGE,V(sensor_id),
+#define ONSENSOR(sensor_id) OPCODE_ONSENSOR,V(sensor_id),
+#define ONBUTTON(sensor_id) OPCODE_ONBUTTON,V(sensor_id),
 #define PAUSE OPCODE_PAUSE,0,0,
 #define PICKUP_STASH(id) OPCODE_PICKUP_STASH,V(id),
 #define PIN_TURNOUT(id,pin,description...) OPCODE_PINTURNOUT,V(id),OPCODE_PAD,V(pin),
diff --git a/EXRAILSensor.cpp b/EXRAILSensor.cpp
new file mode 100644
index 0000000..b0a5fa0
--- /dev/null
+++ b/EXRAILSensor.cpp
@@ -0,0 +1,104 @@
+/*
+ *  © 2024 Chris Harlow
+ *  All rights reserved.
+ *  
+ *  This file is part of CommandStation-EX
+ *
+ *  This is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  It is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**********************************************************************
+EXRAILSensor represents a sensor that should be monitored in order
+to call an exrail ONBUTTON or ONCHANGE handler.
+These are created at EXRAIL startup and thus need no delete or listing
+capability.
+The basic logic is similar to that found in the Sensor class
+except that on the relevant change an EXRAIL thread is started.    
+**********************************************************************/
+
+#include "EXRAILSensor.h"
+#include "EXRAIL2.h"
+
+void EXRAILSensor::checkAll() {
+  if (firstSensor == NULL) return;  // No sensors to be scanned
+  if (readingSensor == NULL) { 
+    // Not currently scanning sensor list
+    unsigned long thisTime = micros();
+    if (thisTime - lastReadCycle < cycleInterval) return;
+    // Required time has elapsed since last read cycle started,
+    // so initiate new scan through the sensor list
+    readingSensor = firstSensor;
+    lastReadCycle = thisTime;
+  }
+  
+  // Loop until either end of list is encountered or we pause for some reason
+  byte sensorCount = 0;
+
+  while (readingSensor != NULL) {
+    bool pause=readingSensor->check();
+    // Move to next sensor in list.
+    readingSensor = readingSensor->nextSensor;
+    // Currently process max of 16 sensors per entry.
+    // Performance measurements taken during development indicate that, with 128 sensors configured
+    // on 8x 16-pin MCP23017 GPIO expanders with polling (no change notification), all inputs can be read from the devices
+    // within 1.4ms (400Mhz I2C bus speed), and a full cycle of checking 128 sensors for changes takes under a millisecond.
+    if (pause || (++sensorCount)>=16) return; 
+  }
+} 
+
+bool EXRAILSensor::check() {
+  // check for debounced change in this sensor 
+  inputState = IODevice::read(pin);
+
+  // Check if changed since last time, and process changes.
+  if (inputState == active) {// no change
+    latchDelay = minReadCount; // Reset counter
+    return false;  // no change 
+  }
+
+    // Change detected ... has it stayed changed for long enough
+    if (latchDelay > 0) {
+      latchDelay--;
+      return false; 
+    } 
+    
+    // change validated, act on it.
+    active = inputState;
+    latchDelay = minReadCount;  // Reset debounce counter
+    if (onChange || active) {
+      new RMFT2(progCounter);
+      return true;  // Don't check any more sensors on this entry
+    }
+    return false; 
+}
+
+EXRAILSensor::EXRAILSensor(VPIN _pin, int _progCounter, bool _onChange) {
+  // Add to the start of the list
+  //DIAG(F("ONthing vpin=%d at %d"), _pin, _progCounter);
+  nextSensor = firstSensor;
+  firstSensor = this;
+
+  pin=_pin;
+  progCounter=_progCounter;
+  onChange=_onChange;
+
+  IODevice::configureInput(pin, true);   
+  active = IODevice::read(pin);
+  inputState = active;
+  latchDelay = minReadCount;
+}
+
+EXRAILSensor *EXRAILSensor::firstSensor=NULL;
+EXRAILSensor *EXRAILSensor::readingSensor=NULL;
+unsigned long EXRAILSensor::lastReadCycle=0;
diff --git a/EXRAILSensor.h b/EXRAILSensor.h
new file mode 100644
index 0000000..b5b00c6
--- /dev/null
+++ b/EXRAILSensor.h
@@ -0,0 +1,50 @@
+/*
+ *  © 2024 Chris Harlow
+ *  All rights reserved.
+ *  
+ *  This file is part of CommandStation-EX
+ *
+ *  This is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  It is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef EXRAILSensor_h
+#define EXRAILSensor_h 
+#include "IODevice.h"
+class EXRAILSensor {
+  static EXRAILSensor * firstSensor;
+ static EXRAILSensor * readingSensor;
+ static unsigned long lastReadCycle;
+ 
+  public:
+  static void checkAll();
+  
+  EXRAILSensor(VPIN _pin, int _progCounter, bool _onChange);
+  bool check();
+  
+  private:
+  static const unsigned int cycleInterval = 10000; // min time between consecutive reads of each sensor in microsecs.
+                                                   // should not be less than device scan cycle time.
+  static const byte minReadCount = 4; // number of additional scans before acting on change
+                                        // E.g. 1 means that a change is ignored for one scan and actioned on the next.
+                                        // Max value is 63
+  
+  EXRAILSensor* nextSensor;
+  VPIN pin; 
+  int progCounter; 
+  bool active; 
+  bool inputState;
+  bool onChange;
+  byte latchDelay;
+};
+#endif
\ No newline at end of file