works, basically

assets/javascripts/stopwatch.js

@@ -0,0 +1,24 @@
+window.Stopwatch = {
+  highlightRunningTimer: function(){
+    $.get(Stopwatch.currentTimerUrl, function(data){
+      if (data.running && data.time_entry_id) {
+        Stopwatch.highlightTimer(data.time_entry_id);
+      }
+    });
+  },
+
+  highlightTimer: function(id){
+    $('table.time-entries tr.time-entry.running').removeClass('running');
+    if(id && id != ''){
+      $('table.time-entries tr.time-entry').each(function(idx, el){
+        var tr = $(el);
+        var trId = tr.attr('id');
+        if (trId && trId == 'time-entry-'+id) {
+          tr.addClass('running');
+        }
+      });
+    }
+  }
+};
+
+$(document).on('ready', Stopwatch.highlightRunningTimer);

assets/stylesheets/stopwatch.css

@@ -0,0 +1,3 @@
+tr.time-entry.running td.hours {
+  color: red;
+}