Amazon Go customers could someday enter the store with a simple wave of the hand, replacing today’s process of swiping in with a dedicated smartphone app.

The U.S. Patent and Trademark Office published a new patent application from Amazon for a “biometric identification system” that includes a hand scanner that can read characteristics such as veins, bones or soft tissue. The application, first reported by Recode, describes scanners placed at entrances and exits of a store linked to an account so that “if the user picks an item from an inventory location and leaves the facility, their account may be billed for that item,” similar to Amazon Go’s signature “Just Walk Out” technology.

Amazon declined to comment.

Drawings within the application show a person standing at a kiosk with two computer-controlled partitions, similar to the entry kiosks in Amazon Go stores that people use an app to open. Several of the inventors listed on the application are Amazon Go executives, engineers and researchers.

Though a lot of the technological innovation of Amazon Go has focused on the customer, the application shows the company is thinking about applying hand-scanning to the back of the house as well. The tech could be used for accepting shipments from suppliers or processing, weighing and scanning items into inventory, per the application.

The first Amazon Go store opened to the public in January 2018, following more than a year of internal testing. Since then, the store count has risen to 25 locations in Seattle, San Francisco, New York and Chicago. One in Chicago and one in San Francisco are already closed for renovations, per the Amazon Go website, a sign the company is evolving the store concept and design.

Technology in patent applications like this one doesn’t always come to fruition, but it gives a glimpse into concepts companies like Amazon are thinking about. The application represents the latest indication that Amazon is interested in using biometric identification for shoppers, following a report in September that the tech giant was testing a system to let customers pay for items at Whole Foods stores using hand scans.

The use of biometric data, specifically facial recognition technology, by U.S. tech giants has become a controversial topic. Stephanie Hare, an independent researcher who specializes in technology ethics, told the New York Post in September it appeared that Amazon decided customers would be more likely to accept palm readers than a payment solution based on facial recognition.

Though it hasn’t become mainstream, palm-scanning is not exactly a new technology. Consumer advocates were warning about how the use of biometric data like hand-scanning could put people in danger of identity theft years ago. And it has been used in a variety of areas, from school lunch rooms to doctors offices.