At least two companies are offering wristbands they say will allow people to demonstrate that they have received a shot—though the method and standards of proof vary and the bands are not endorsed by federal health bodies.

ImmunaBand, which launched its silicone bracelet of the same name on March 15, claims to have released the “first-to-market wearable COVID-19 vaccination documentation”.

Each ImmunaBand, priced at $19.99, has a metal tag with a unique QR code attached to it which, when scanned, links to a copy of the wearer’s vaccination card. A more expensive one is available which has the wearer’s name and vaccine type engraved on it. Both are sold on the ImmunaBand website.

ImmunaBand requires that people upload a photograph of their vaccination card to an ImmunaBand server. The company says this photo is stored and end-to-end encrypted “to ensure data privacy and security.” It is also protected with a password.

J. Tashof Bernton, president of ImmunaBand, said in a statement that “quick, easy access to documentation of vaccination status is lacking” and added the bracelet served as a “passport.”

In at least one case the bands have been taken on by hospitality staff. Some workers at the El Merkury Central American Street Food outlet in Philadelphia have started to wear them, and the business owner, Sofia DeLeon, told CNN affiliate WPVI that “it was really important for me to have everybody be vaccinated.”

ImmunaBand states that customer information goes through approval before bracelets are shipped out, but does not specify whether any system is in place to detect a forged vaccine card. Newsweek has contacted ImmunaBand for comment.

Last week Forbes reported that fake vaccine cards were on the rise and that a CVS employee in New York was arrested for stealing vaccine cards to redistribute fraudulently.

Meanwhile, vaccine bracelets are also being sold by another company, Covid Verified, which does not require users to upload any proof of vaccination.

The company states the $12.95 bracelets, available on the Covid Verified website, work on an “honor system,” under which wearers sign a pledge to say that they have had the vaccine but do not have to provide any documentation.

In total, 157,132,234 U.S. citizens have now received a COVID-19 vaccine according to the most recent data by the Centers for Disease Control and Prevention at the time of writing. Some 344,503,495 doses have been delivered.

It means that just under half the U.S. population has had at least one dose of a vaccine, and 84.8 percent of U.S. citizens aged 65 or older have had at least one dose.