You want to look into Car Secure Access if you want to use the car calls as an access code. Typically you also need a three position keyswitch to secure and unsecure the floor and enter the access code. You could fake out the keyswitch when setting up, because if adding the keyswitch for one floor you would be better to just use floor lockout. There is a couple other options you could do depending on how the customer wants it to work.