diff --git a/src/server/dev.ts b/src/server/dev.ts
index 6e078422..9cb63415 100644
--- a/src/server/dev.ts
+++ b/src/server/dev.ts
@@ -3,6 +3,8 @@ import * as history from 'connect-history-api-fallback'
 import * as express from 'express'
 import * as http from 'http'
 import * as minimist from 'minimist'
+import { reaction } from 'mobx'
+import { IObservableValue } from 'mobx'
 import * as favicon from 'serve-favicon'
 import * as sio from 'socket.io'
 import * as webpack from 'webpack'
@@ -34,9 +36,10 @@ const server = http.createServer(app)
 const sioNetwork = sio(server, { parser: NUClearNetProxyParser } as any)
 
 // Initialize socket.io namespace immediately to catch reconnections.
-WebSocketProxyNUClearNetServer.of(WebSocketServer.of(sioNetwork.of('/nuclearnet')), {
-  fakeNetworking: withVirtualRobots,
-})
+const webSocketProxyNUClearNetServer = WebSocketProxyNUClearNetServer.of(
+  WebSocketServer.of(sioNetwork.of('/nuclearnet')),
+  { fakeNetworking: withVirtualRobots },
+)
 
 const devMiddleware = webpackDevMiddleware(compiler, {
   publicPath: '/',
@@ -73,7 +76,21 @@ function init() {
         { frequency: 60, simulator: ChartSimulator.of() },
       ],
     })
-    virtualRobots.startSimulators()
+    let stopSimulators: () => void | undefined
+    reaction(
+      () => webSocketProxyNUClearNetServer.numConnections > 0,
+      enable => {
+        if (enable) {
+          // tslint:disable-next-line no-console
+          console.log('Client connected, starting simulator')
+          stopSimulators = virtualRobots.startSimulators()
+        } else if (stopSimulators) {
+          // tslint:disable-next-line no-console
+          console.log('No clients remain connected, stopping simulator')
+        }
+      },
+      { fireImmediately: true },
+    )
   }
 
   if (nbsFile) {
diff --git a/src/server/nuclearnet/web_socket_proxy_nuclearnet_server.ts b/src/server/nuclearnet/web_socket_proxy_nuclearnet_server.ts
index e164651d..a260e896 100644
--- a/src/server/nuclearnet/web_socket_proxy_nuclearnet_server.ts
+++ b/src/server/nuclearnet/web_socket_proxy_nuclearnet_server.ts
@@ -1,3 +1,5 @@
+import { action } from 'mobx'
+import { observable } from 'mobx'
 import { NUClearNetOptions } from 'nuclearnet.js'
 import { NUClearNetPeer } from 'nuclearnet.js'
 import { NUClearNetPacket } from 'nuclearnet.js'
@@ -21,6 +23,8 @@ type Opts = {
  * improved to have more intelligent multiplexing.
  */
 export class WebSocketProxyNUClearNetServer {
+  @observable numConnections: number = 0
+
   constructor(private server: WebSocketServer, private nuclearnetClient: NUClearNetClient) {
     server.onConnection(this.onClientConnection)
   }
@@ -30,8 +34,11 @@ export class WebSocketProxyNUClearNetServer {
     return new WebSocketProxyNUClearNetServer(server, nuclearnetClient)
   }
 
-  private onClientConnection = (socket: WebSocket) => {
+  @action.bound
+  private onClientConnection(socket: WebSocket) {
+    this.numConnections++
     WebSocketServerClient.of(this.nuclearnetClient, socket)
+    socket.onDisconnect(action(() => this.numConnections--))
   }
 }
 
@@ -149,9 +156,9 @@ class PacketProcessor {
       this.sendReliablePacket(event, packet)
     } else if (this.isEventBelowLimit(event)) {
       this.sendUnreliablePacket(event, packet)
-    }/* else {
-      // This event is unreliable and already at the limit, simply drop the packet.
-    }*/
+    } else {
+      return // The event is unreliable and already at the limit, simply drop the packet.
+    }
   }
 
   private isEventBelowLimit(event: string) {
diff --git a/src/server/nuclearnet/web_socket_server.ts b/src/server/nuclearnet/web_socket_server.ts
index b4b9c1e8..1638bfcc 100644
--- a/src/server/nuclearnet/web_socket_server.ts
+++ b/src/server/nuclearnet/web_socket_server.ts
@@ -34,6 +34,10 @@ export class WebSocket {
     this.sioSocket.on(event, cb)
   }
 
+  onDisconnect(cb: () => void) {
+    this.on('disconnect', cb)
+  }
+
   send(event: string, ...args: any[]) {
     this.sioSocket.emit(event, ...args)
   }
diff --git a/src/server/prod.ts b/src/server/prod.ts
index f33dc00c..797cc65d 100644
--- a/src/server/prod.ts
+++ b/src/server/prod.ts
@@ -3,6 +3,7 @@ import * as history from 'connect-history-api-fallback'
 import * as express from 'express'
 import * as http from 'http'
 import * as minimist from 'minimist'
+import { reaction } from 'mobx'
 import * as favicon from 'serve-favicon'
 import * as sio from 'socket.io'
 
@@ -34,6 +35,11 @@ server.listen(port, () => {
   console.log(`NUsight server started at http://localhost:${port}`)
 })
 
+const webSocketProxyNUClearNetServer = WebSocketProxyNUClearNetServer.of(
+  WebSocketServer.of(sioNetwork.of('/nuclearnet')),
+  { fakeNetworking: withVirtualRobots },
+)
+
 if (withVirtualRobots) {
   const virtualRobots = VirtualRobots.of({
     fakeNetworking: true,
@@ -44,9 +50,19 @@ if (withVirtualRobots) {
       { frequency: 10, simulator: ChartSimulator.of() },
     ],
   })
-  virtualRobots.startSimulators()
+  let stopSimulators: () => void | undefined
+  reaction(
+    () => webSocketProxyNUClearNetServer.numConnections > 0,
+    enable => {
+      if (enable) {
+        // tslint:disable-next-line no-console
+        console.log('Client connected, starting simulator')
+        stopSimulators = virtualRobots.startSimulators()
+      } else if (stopSimulators) {
+        // tslint:disable-next-line no-console
+        console.log('No clients remain connected, stopping simulator')
+      }
+    },
+    { fireImmediately: true },
+  )
 }
-
-WebSocketProxyNUClearNetServer.of(WebSocketServer.of(sioNetwork.of('/nuclearnet')), {
-  fakeNetworking: withVirtualRobots,
-})