--- a/svghmi/gen_index_xhtml.xslt	Wed Jun 30 15:51:59 2021 +0200
+++ b/svghmi/gen_index_xhtml.xslt	Thu Jul 01 14:33:14 2021 +0200
@@ -7556,7 +7556,19 @@
 </xsl:text>
           <xsl:text>// Open WebSocket to relative "/ws" address
 </xsl:text>
-          <xsl:text>var ws = new WebSocket(window.location.href.replace(/^http(s?:\/\/[^\/]*)\/.*$/, 'ws$1/ws'));
+          <xsl:text>
+</xsl:text>
+          <xsl:text>var ws_url = 
+</xsl:text>
+          <xsl:text>    window.location.href.replace(/^http(s?:\/\/[^\/]*)\/.*$/, 'ws$1/ws')
+</xsl:text>
+          <xsl:text>    + '?mode=' + (window.location.hash == "#watchdog" 
+</xsl:text>
+          <xsl:text>                  ? "watchdog"
+</xsl:text>
+          <xsl:text>                  : "multiclient");
+</xsl:text>
+          <xsl:text>var ws = new WebSocket(ws_url);
 </xsl:text>
           <xsl:text>ws.binaryType = 'arraybuffer';
 </xsl:text>

--- a/svghmi/svghmi.js	Wed Jun 30 15:51:59 2021 +0200
+++ b/svghmi/svghmi.js	Thu Jul 01 14:33:14 2021 +0200
@@ -30,7 +30,13 @@
 };
 
 // Open WebSocket to relative "/ws" address
-var ws = new WebSocket(window.location.href.replace(/^http(s?:\/\/[^\/]*)\/.*$/, 'ws$1/ws'));
+
+var ws_url = 
+    window.location.href.replace(/^http(s?:\/\/[^\/]*)\/.*$/, 'ws$1/ws')
+    + '?mode=' + (window.location.hash == "#watchdog" 
+                  ? "watchdog"
+                  : "multiclient");
+var ws = new WebSocket(ws_url);
 ws.binaryType = 'arraybuffer';
 
 const dvgetters = {

--- a/svghmi/svghmi_server.py	Wed Jun 30 15:51:59 2021 +0200
+++ b/svghmi/svghmi_server.py	Thu Jul 01 14:33:14 2021 +0200
@@ -120,6 +120,10 @@
         self._hmi_session = None
         WebSocketServerProtocol.__init__(self, *args, **kwargs)
 
+    def onConnect(self, request):
+        self.has_watchdog = request.params.get("mode", [None])[0] == "watchdog"
+        return WebSocketServerProtocol.onConnect(self, request)
+
     def onOpen(self):
         assert(self._hmi_session is None)
         self._hmi_session = HMISession(self)