The default acknowledgement code for a Sensaphone Auto Dialer is 555, if you did not personalize or change the code on installation. Check out all of the Senaphone AutoDialer units at the below links: USA: http://www.absoluteautomation.com/brands/Sensaphone.html CANADA: http://www.absoluteautomation.ca/sensaphone-alarms-s/1867.htm