Update content offline on mobile

Update content offline on mobile

The client wants to scan barcodes in his inventories, and to see the inventory scanned in real time.
He uses a mobile phone and an external barcode reader, which just pastes the barcode value with a line break in the end.
The challenge here is to make this work offline, since some of the warehouses don't have internet available.

I tried creating a page with a stateless form and a report, which on every scan the "on user input" workflow is triggered. adds a record, reloads the page to show the updated report.
This is pretty slow, and can't work offline since "on user input" don't run when offline.

I also tried using a form with a subform, but the subform's content is not available in real time - the user needs to press it in order to see the content.

I would be happy to get more ideas on how to solve this.