diff --git a/desktop/app.go b/desktop/app.go
index 6369d09..4bf36f1 100644
--- a/desktop/app.go
+++ b/desktop/app.go
@@ -124,6 +124,23 @@ func (a *App) startup(ctx context.Context) {
 	})
 
 	a.startPipeline(ctx)
+
+	// Recognition starts with the app. Until this, the engine only ever
+	// started when somebody pressed Start - which meant a till that rebooted
+	// overnight came back with the window open, the tray icon showing, the
+	// session restored, and recognition off until a shop assistant noticed.
+	// That is the failure the tray colours exist to catch, and it should not
+	// be the default state every morning.
+	//
+	// Guarded on the interpreter actually being there: on a PC where setup has
+	// not run yet, starting the supervisor would loop on a missing executable
+	// with nothing useful to say. The Start button still exists for the one
+	// case where somebody has deliberately stopped it.
+	if _, err := os.Stat(exe); err == nil {
+		a.sup.Start()
+	} else {
+		log.Printf("engine not installed yet (%s); run behavision-setup, then Start", exe)
+	}
 }
 
 // webhookURL is the loopback address the bridge is listening on, or empty