Amazon, DHL and FedEx are building drones that deliver packages to your door. IBM, however, envisions a future where drones steal them instead.

The computing giant won a patent on Nov. 12 for “Preventing anonymous theft by drones” with an Internet of Things (IoT) altimeter that triggers upon liftoff, tracking the package’s altitude and uploading the data to a blockchain platform.

The patent seeks to get ahead of two modern realities: people buy goods online, and people fly their own personal drones. That could be a problem, it says, if the trends combine to devious ends.

“The confluence of the increase in drone use and the increase in online shopping provides a situation in which a drone may be used with nefarious intent to anonymously take a package that is left on a doorstep after delivery,” the patent description reads.

IBM’s solution is to outfit packages with an IoT sensor that only triggers if it detects a change in altitude “exceeding the threshold … expected when the object is lifted away by a drone.” Once it does, the sensor periodically updates the blockchain, and the intended recipient, with the package’s altitude.

To be clear, there’s no indication that IBM actually plans to build an operational device. And if it does, it may well swap out a blockchain for some other “secure database,” according to the patent.

But the description does say blockchain is the patent’s “preferred embodiment,” in part because it allows disparate “trusted entities” – the merchant, the shipper, etc. – to input the package’s whereabouts.

It is unclear how prevalent drone heists are in America. At the moment, most shipping companies are focused on building delivery mechanisms.