I was wondering something about custom field/custom modules in Zoho Desk.

For some reason you can make a custom field mandatory but not unique?

For example, if I create a custom module to manage equipment and renewal and make a field serial number no way to make this field unique to make sure we don’t have double?

For example, in the CRM you can set a field to prevent duplicate.

So, looking for suggestions to prevent people having entered the same device multiple times.  

I am pretty sure I am screwed but maybe I am just missing something.