diff --git a/klingel_sender_nano_serial/doorbell.py b/klingel_sender_nano_serial/doorbell.py
index 3c8533a..0b5d105 100644
--- a/klingel_sender_nano_serial/doorbell.py
+++ b/klingel_sender_nano_serial/doorbell.py
@@ -1,4 +1,7 @@
 # https://www.instructables.com/id/Arduino-Python-Communication-via-USB/
+# in rc.local:
+#   su tilman -c 'python3 /media/hd/admin/doorbell/doorbell.py >> /media/hd/admin/doorbell/doorbell.log 2>&1 &'
+
 import serial
 import urllib.request
 import logging