Amazon has come under fire after a patent application emerged that would allow the company’s Echo speaker to listen for certain key words during people’s conversations.

The patent, filed in the US, describes how the speaker would employ ‘vocal-sniffing’ technology to listen for key words, Amazon could then start deploying advertising that would target those words.

In response, Amazon said the patent did not represent any current plans the technology giant had.

“We take privacy seriously and have built multiple layers of privacy into our Echo devices,” an Amazon spokesman said.

“We do not use customers’ voice recordings for targeted advertising. 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.”

Amazon is behind the Echo range of popular smart home speakers – which are powered by virtual assistant Alexa – and which respond to commands when the trigger word “Alexa” is said.

Users can then ask for music, set timers and get news and weather information.

However, the new patent describes a more broad listening tool that would be capable of “capturing voice content, such as when a user speaks into or near a device” and then identifying trigger words that “indicate a level of interest of the user”.

Facebook has also been the subject of speculation that it uses the microphones built into devices to listen to user conversations and target them with relevant adverts.

However, when asked by members of the US Congress during a committee appearance on Tuesday if the site used such a practice, the social network’s founder Mark Zuckerberg replied “No”.

“You’re talking about this conspiracy theory that gets passed around that we listen to what’s going on, on your microphone and use that for ads. We don’t do that,” he added.