Serial Number field
Every Record that is added in ActivityInfo is automatically assigned a unique, randomly-generated ID (e.g. "c23cwexxsf") when it is created. However, in many situations, it can be useful to identify Records by easier-to-remember sequential numbers such as "000023", "000024". So this is the format that a Serial Number will have in Data Entry if you add a Serial Number field in your Form.
Instead of just having a number, which is not very easy to trace or remember, you can add a Prefix Formula to the Serial Number. This will give more traceability to it without revealing sensitive information.
In order to ensure that Serial Numbers are unique, they are only assigned once the Record is actually saved on the server. When you are adding a Record, the Serial Number will be displayed as "(Pending)".
If you save a Record while you are working offline, a Serial Number will not be assigned until you have fully synchronised the Form to ActivityInfo.
You can only have one Serial Number field in a Form. If you have a Serial Number field in your Form, this is automatically the Key of your Form.
By default, ActivityInfo assigns a serial number using the format '%06d' which is 6 digits with padding with zeros.
Serial numbers can be particularly useful in setting up Case Tracking Systems, where case workers need an easy-to-remember identifier for each case that doesn't include personally-identifying information.