Tech giant Amazon is offering $10 in promotional credit if you enroll your palm prints in its checkout-free stores and link it to your Amazon account, media reports said on Tuesday.

Last year, Amazon introduced its new biometric palm print scanner, Amazon One, so customers can pay for goods in some stores by waving their palm prints over one of these scanners.

By February, the company expanded its palm scanners to other Amazon grocery, book, and 4-star stores across Seattle reports TechCrunch.

According to the report, Amazon has since expanded its biometric scanning technology to its stores across the US, including in New York, New Jersey, Maryland, and Texas.

The retail and cloud giant said its palm scanning hardware “captures the minute characteristics of your palm — both surface-area details like lines and ridges as well as subcutaneous features such as vein patterns — to create your palm signature,” which is then stored in the cloud and used to confirm your identity when you are in one of its stores.

The report said that palm print on its own might not do much — though Amazon said it uses an unspecified “subset” of anonymous palm data to improve the technology. But by linking it to your Amazon account, Amazon can use the data it collects, like shopping history, to target ads, offers, and recommendations to you over time.

Amazon also said it stores palm data indefinitely, unless you choose to delete the data once there are no outstanding transactions left, or if you don’t use the feature for two years, the report said.