Soon after Mark Zuckerberg was once again forced to deny that Facebook secretly listened in on users' conversations to improve ad targeting, a recently filed Amazon patent was discovered that appears to perform a similar function.

The patent describes how Amazon's digital assistant, Alexa, could listen out for certain trigger words, such as "love," "like," and "hate," that will help it ascertain a user's preferences and dislikes---very helpful when it comes to targeted ads. "One or more sniffer algorithms or processes can attempt to identify trigger words in the voice content, which can indicate a level of interest of the user," states the document.

While the technology may be used to expand an Amazon user's profile and discover what advertisements might be of interest to them, it could also see Alexa acting without first being prompted. "If the user mentions how much the user would like to go to a restaurant while on the phone, a recommendation might be sent while the user is still engaged in the conversation that enables the user to make a reservation at the restaurant," suggests the patent.

Such abilities do raise a multitude of privacy concerns, particularly at a time when the practice of tech companies spying on their users is under the spotlight. But as with all patents, there's no guarantee that this one will ever become a reality.

"We take privacy seriously and have built multiple layers of privacy into our Echo devices," Amazon said, in a statement to the BBC.

"Like many companies, we file a number of forward-looking patent applications that explore the full possibilities of new technology. Patents take multiple years to receive and do not necessarily reflect current developments to products and services."

Earlier this week, Mark Zuckerberg assured Sen. Gary Peters that Facebook did not secretly use device microphones to record users as a way of serving them appropriate ads---a conspiracy theory that's been around for years.