Untraceable Command

Untraceable Command

The Untraceable command is a privacy feature introduced in the epc-gen2/" class="glossary-term-link" data-term="EPC Gen2" data-definition="UHF RFID air interface standard." data-category="Standards & Protocols">EPC Gen2 version 2 (Gen2v2) specification. It allows an RFID reader to selectively hide portions of a tag's data and reduce its operating range, effectively making the tag invisible or partially invisible to standard readers. Untraceable was designed as a more flexible alternative to the Kill Command — it protects consumer privacy without permanently destroying the tag.

What Untraceable Controls

The Untraceable command can modify four aspects of tag behaviour:

These features can be applied independently or in combination. For example, a retailer might truncate the EPC to hide the serial number while keeping the company prefix visible, and reduce the range to prevent tracking beyond a few centimetres.

How It Works

Untraceable operates as a tag state transition. The reader sends the Untraceable command with the desired configuration and the tag's Access Password. Once applied, the tag's behaviour changes persistently — the restrictions survive power loss and remain in effect until an authorised reader sends a new Untraceable command to restore full visibility.

The range reduction feature works by increasing the tag's effective sensitivity threshold. The tag IC deliberately requires more power to activate, which means only readers in very close proximity can energise it. This physical limitation cannot be bypassed by a high-power rogue reader because the tag itself enforces the constraint.

Privacy Applications

Retail point of sale: When a customer purchases a garment with an embedded RFID inlay, the POS system can apply Untraceable to hide the EPC serial number and reduce range. The tag remains functional for returns (the store reader knows the Access Password) but is invisible to third-party scanners.

GDPR compliance: European privacy regulations may require that personally-linkable RFID data be obscured after sale. Untraceable provides a technical mechanism to demonstrate compliance without destroying the tag.

Untraceable vs. Kill

Untraceable is preferred in most modern deployments because it preserves the option for returns, warranty claims, and circular economy applications. The Kill Command remains available as a last resort for scenarios requiring absolute assurance that a tag can never be read again.

Tag IC Support

Not all tag ICs support Untraceable. It requires Gen2v2-compliant silicon. NXP UCODE 8 and newer Impinj ICs include Untraceable capability. Legacy Gen2v1 tags do not support this feature and can only be protected via Kill or Protected Mode.