# Detect Duplicate Barcodes

In the mobile app go to: Settings → Accept duplicate barcodes and pick the behavior that matches your workflow:

Ask every time Prompts you whenever a scanned value already appeared during the current session. Good for mixed scenarios where some duplicates are legitimate.
Always accept All scans are sent, even if repeated. Fastest option; no filtering.
Discard adjacent Ignores an immediate repeat of the previous barcode (protects against the scanner reading the same label twice while still pointing at it).
Discard scan session Each distinct barcode value is accepted only once for the whole session. Later repeats are silently ignored.

# Advanced (Output Templates)

For fine-grained control (e.g., blocking duplicates with custom warning messages), configure an Output Template with:

A BARCODE component to capture the value
A JAVASCRIPT_FUNCTION component to store scanned values in localStorage
An IF + ENDIF block to conditionally display an ALERT ("Duplicate detected – scan a different code")

This device-side logic enables duplicate prevention, operator alerts, and output suppression without requiring server connectivity.