The voice recognition software allows users to control the television with a series of commands
Families are being warned that modern televisions are recording their conversations and could transmit the messages to "third parties".
Many of the latest sets have microphones so viewers can change channel, turn on a DVD or browse the internet by speaking at the screen or remote.
But the small print of the privacy policies for these so-called Smart TVs contain warnings that general conversations are also being recorded.
Television companies advise users who are concerned to avoid discussing "personal" matters in their livings rooms.
The practice, which emerged on internet forums yesterday, led customers on social media to draw comparisons to George Orwell's 1984.
Emma Carr, director of campaign group Big Brother Watch, said: "Not everyone wants to be spied on by their TV.
"Few people would expect a TV to intrude on our privacy, yet this is increasingly becoming the case. As this sort of technology is being made to gather increasing amounts of data about us, it is vitally important that people should have to choose to make use of these additional services."
The technology works by converting words into text commands. If these are simple, such as for changing a channel, they do not need to be sent over the internet. But for more complex requests, such as finding the details of a film on Google, the information is transmitted online to a separate company.
A customer could, for instance, ask: "what period drama programs are on television tonight?". Results should appear on the screen with a list of options.
It is unclear whether the information is used for marketing purposes or held on computer that could be hacked by criminals.
In Orwell's 1984, written in the late Forties, protagonist Winston Smith was monitored by a "telescreen" broadcasting propaganda messages and recording his movements, while "every sound you made was overhead" by the Thought Police.
The privacy policy for South Korean manufacturer Samsung, one of the most popular television brands in Britain, states: "Please be aware that if your spoken words include personal or other sensitive information, that information will be among the data captured and transmitted to a third party."
According to the Daily Beast website, the document indicates that some recordings may still be made even if the viewer switches off the equipment.
"If you do not enable Voice Recognition... while Samsung will not collect your spoken word, Samsung may still collect associated texts and other usage data so that we can evaluate the performance of the feature and improve it," it states.
Samsung played down the dangers. A spokesman said an icon should appear on the screen when voice recognition is on.
"Our TV’s don’t passively record conversations. You must press the mic button on the remote to ask a question – just like on a smartphone."
In a statement, the company said: "Samsung takes consumer privacy very seriously.
"We employ industry-standard security safeguards and practices, including data encryption, to secure consumers’ personal information and prevent unauthorized collection or use.
"Samsung does not sell voice data to third parties. If a consumer consents and uses the voice recognition feature, voice data is provided to a third party during a requested voice command search. At that time, the voice data is sent to a server, which searches for the requested content then returns the desired content to the TV."
The spokesman could not confirm whether the data was used for other purposes by its third-party provider.