diff --git a/field/plc.go b/field/plc.go
index 185f16b..9441161 100644
--- a/field/plc.go
+++ b/field/plc.go
@@ -13,14 +13,18 @@ import (
 )
 
 type Plc struct {
-	IsHealthy    bool
-	address      string
-	handler      *modbus.TCPClientHandler
-	client       modbus.Client
-	Inputs       [inputCount]bool
-	Registers    [registerCount]uint16
-	Coils        [coilCount]bool
-	cycleCounter int
+	IsHealthy        bool
+	address          string
+	handler          *modbus.TCPClientHandler
+	client           modbus.Client
+	Inputs           [inputCount]bool
+	Registers        [registerCount]uint16
+	Coils            [coilCount]bool
+	oldInputs        [inputCount]bool
+	oldRegisters     [registerCount]uint16
+	oldCoils         [coilCount]bool
+	IoChangeNotifier *Notifier
+	cycleCounter     int
 }
 
 const (
@@ -100,6 +104,8 @@ func (plc *Plc) SetAddress(address string) {
 
 // Loops indefinitely to read inputs from and write outputs to PLC.
 func (plc *Plc) Run() {
+	plc.IoChangeNotifier = NewNotifier()
+
 	for {
 		if plc.handler == nil {
 			if plc.address == "" {
@@ -131,6 +137,14 @@ func (plc *Plc) Run() {
 			plc.cycleCounter = 0
 		}
 
+		// Detect any changes in input or output and notify listeners if so.
+		if plc.Inputs != plc.oldInputs || plc.Registers != plc.oldRegisters || plc.Coils != plc.oldCoils {
+			plc.IoChangeNotifier.Notify(nil)
+			plc.oldInputs = plc.Inputs
+			plc.oldRegisters = plc.Registers
+			plc.oldCoils = plc.Coils
+		}
+
 		time.Sleep(time.Until(startTime.Add(time.Millisecond * plcLoopPeriodMs)))
 	}
 }
diff --git a/static/js/setup_field.js b/static/js/setup_field.js
new file mode 100644
index 0000000..e349b3f
--- /dev/null
+++ b/static/js/setup_field.js
@@ -0,0 +1,28 @@
+// Copyright 2018 Team 254. All Rights Reserved.
+// Author: pat@patfairbank.com (Patrick Fairbank)
+//
+// Client-side logic for the field setup page.
+
+var websocket;
+
+// Handles a websocket message to update the PLC IO status.
+var handlePlcIoChange = function(data) {
+  $.each(data.Inputs, function(index, input) {
+    $("#input" + index).text(input)
+  });
+
+  $.each(data.Registers, function(index, register) {
+    $("#register" + index).text(register)
+  });
+
+  $.each(data.Coils, function(index, coil) {
+    $("#coil" + index).text(coil)
+  });
+};
+
+$(function() {
+  // Set up the websocket back to the server.
+  websocket = new CheesyWebsocket("/setup/field/websocket", {
+    plcIoChange: function(event) { handlePlcIoChange(event.data); }
+  });
+});
diff --git a/templates/setup_field.html b/templates/setup_field.html
index 0a3f67f..55453d7 100644
--- a/templates/setup_field.html
+++ b/templates/setup_field.html
@@ -44,10 +44,10 @@
             <tr>
               <th colspan="2">Inputs</th>
             </tr>
-            {{range $i, $value := .Inputs}}
+            {{range $i, $name := .InputNames}}
             <tr>
-              <td>{{index $.InputNames $i}}</td>
-              <td>{{$value}}</td>
+              <td>{{$name}}</td>
+              <td id="input{{$i}}"></td>
             </tr>
             {{end}}
           </table>
@@ -57,10 +57,10 @@
             <tr>
               <th colspan="2">Registers</th>
             </tr>
-            {{range $i, $value := .Registers}}
+            {{range $i, $name := .RegisterNames}}
             <tr>
-              <td>{{index $.RegisterNames $i}}</td>
-              <td>{{$value}}</td>
+              <td>{{$name}}</td>
+              <td id="register{{$i}}"></td>
             </tr>
             {{end}}
           </table>
@@ -70,10 +70,10 @@
             <tr>
               <th colspan="2">Coils</th>
             </tr>
-            {{range $i, $value := .Coils}}
+            {{range $i, $name := .CoilNames}}
             <tr>
-              <td>{{index $.CoilNames $i}}</td>
-              <td>{{$value}}</td>
+              <td>{{$name}}</td>
+              <td id="coil{{$i}}"></td>
             </tr>
             {{end}}
           </table>
@@ -101,4 +101,5 @@
 </div>
 {{end}}
 {{define "script"}}
+<script src="/static/js/setup_field.js"></script>
 {{end}}
diff --git a/web/setup_field.go b/web/setup_field.go
index f50402b..1b4a891 100644
--- a/web/setup_field.go
+++ b/web/setup_field.go
@@ -9,6 +9,7 @@ import (
 	"github.com/Team254/cheesy-arena/field"
 	"github.com/Team254/cheesy-arena/led"
 	"github.com/Team254/cheesy-arena/model"
+	"log"
 	"net/http"
 	"strconv"
 )
@@ -28,17 +29,13 @@ func (web *Web) fieldGetHandler(w http.ResponseWriter, r *http.Request) {
 	data := struct {
 		*model.EventSettings
 		AllianceStationDisplays map[string]string
-		Inputs                  []bool
 		InputNames              []string
-		Registers               []uint16
 		RegisterNames           []string
-		Coils                   []bool
 		CoilNames               []string
 		CurrentLedMode          led.Mode
 		LedModeNames            map[led.Mode]string
-	}{web.arena.EventSettings, web.arena.AllianceStationDisplays, plc.Inputs[:], plc.GetInputNames(), plc.Registers[:],
-		plc.GetRegisterNames(), plc.Coils[:], plc.GetCoilNames(), web.arena.ScaleLeds.GetCurrentMode(),
-		led.ModeNames}
+	}{web.arena.EventSettings, web.arena.AllianceStationDisplays, plc.GetInputNames(), plc.GetRegisterNames(),
+		plc.GetCoilNames(), web.arena.ScaleLeds.GetCurrentMode(), led.ModeNames}
 	err = template.ExecuteTemplate(w, "base", data)
 	if err != nil {
 		handleWebErr(w, err)
@@ -88,3 +85,54 @@ func (web *Web) fieldTestPostHandler(w http.ResponseWriter, r *http.Request) {
 
 	http.Redirect(w, r, "/setup/field", 303)
 }
+
+// The websocket endpoint for sending realtime updates to the field setup page.
+func (web *Web) fieldWebsocketHandler(w http.ResponseWriter, r *http.Request) {
+	if !web.userIsAdmin(w, r) {
+		return
+	}
+
+	websocket, err := NewWebsocket(w, r)
+	if err != nil {
+		handleWebErr(w, err)
+		return
+	}
+	defer websocket.Close()
+
+	plcIoChangeListener := web.arena.Plc.IoChangeNotifier.Listen()
+	defer close(plcIoChangeListener)
+
+	// Send the PLC status immediately upon connection.
+	data := struct {
+		Inputs    []bool
+		Registers []uint16
+		Coils     []bool
+	}{web.arena.Plc.Inputs[:], web.arena.Plc.Registers[:], web.arena.Plc.Coils[:]}
+	err = websocket.Write("plcIoChange", data)
+	if err != nil {
+		log.Printf("Websocket error: %s", err)
+		return
+	}
+
+	for {
+		var messageType string
+		var message interface{}
+		select {
+		case _, ok := <-plcIoChangeListener:
+			if !ok {
+				return
+			}
+			messageType = "plcIoChange"
+			message = struct {
+				Inputs    []bool
+				Registers []uint16
+				Coils     []bool
+			}{web.arena.Plc.Inputs[:], web.arena.Plc.Registers[:], web.arena.Plc.Coils[:]}
+		}
+		err = websocket.Write(messageType, message)
+		if err != nil {
+			// The client has probably closed the connection; nothing to do here.
+			return
+		}
+	}
+}
diff --git a/web/web.go b/web/web.go
index 1f05ea3..685316d 100644
--- a/web/web.go
+++ b/web/web.go
@@ -152,6 +152,7 @@ func (web *Web) newHandler() http.Handler {
 	router.HandleFunc("/setup/field", web.fieldPostHandler).Methods("POST")
 	router.HandleFunc("/setup/field/reload_displays", web.fieldReloadDisplaysHandler).Methods("GET")
 	router.HandleFunc("/setup/field/test", web.fieldTestPostHandler).Methods("POST")
+	router.HandleFunc("/setup/field/websocket", web.fieldWebsocketHandler).Methods("GET")
 	router.HandleFunc("/setup/lower_thirds", web.lowerThirdsGetHandler).Methods("GET")
 	router.HandleFunc("/setup/lower_thirds/websocket", web.lowerThirdsWebsocketHandler).Methods("GET")
 	router.HandleFunc("/setup/sponsor_slides", web.sponsorSlidesGetHandler).Methods("GET")