diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 0af40cfc7..8d2652e0a 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -95,6 +95,7 @@ import (
 	"tailscale.com/types/preftype"
 	"tailscale.com/types/ptr"
 	"tailscale.com/types/views"
+	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/deephash"
 	"tailscale.com/util/dnsname"
 	"tailscale.com/util/goroutines"
@@ -2863,6 +2864,9 @@ func (b *LocalBackend) WatchNotificationsAs(ctx context.Context, actor ipnauth.A
 	mak.Set(&b.notifyWatchers, sessionID, session)
 	b.mu.Unlock()
 
+	metricCurrentWatchIPNBus.Add(1)
+	defer metricCurrentWatchIPNBus.Add(-1)
+
 	defer func() {
 		b.mu.Lock()
 		delete(b.notifyWatchers, sessionID)
@@ -7696,3 +7700,7 @@ func (b *LocalBackend) vipServicesFromPrefsLocked(prefs ipn.PrefsView) []*tailcf
 
 	return slicesx.MapValues(services)
 }
+
+var (
+	metricCurrentWatchIPNBus = clientmetric.NewGauge("localbackend_current_watch_ipn_bus")
+)