Your television knows what you watched last night, and roughly how long you watched it. That is not a conspiracy theory. It is a feature called automatic content recognition, and it arrives switched on by default on most sets sold in Britain.

The set takes a fingerprint of whatever is on screen — a few frames of pixel data, or a snippet of audio — every few seconds, matches it against a database of programmes and adverts, and reports the result back to the manufacturer or one of its partners. That feeds recommendations for you, and advertising profiles about you.

The good news is that most of it can be turned off in about ten minutes. The rest can be starved of data at the router, which matters because smart TV settings menus move around with every firmware update and occasionally reset themselves.

What is actually being collected

Three separate mechanisms usually get bundled together, and it helps to keep them apart.

• Automatic content recognition (ACR). The screen or the speakers are sampled and matched against a content database. It works on live TV, on streaming apps and, on some sets, on anything you plug into an HDMI port.
• Advertising identifiers. A resettable ID attached to your set, shared with apps and ad networks so the same household can be recognised across services.
• Voice and usage data. Commands spoken into a remote, plus logs of which apps you opened and when.

Turn off the first two and your set becomes much duller. Turn off all three and it is about as talkative as a monitor.

Switching off ACR, platform by platform

Menu wording shifts between model years, so treat the paths below as a map rather than a script. If you cannot find a setting, search the set's own help pages using the name of the feature.

Samsung

Open Settings > All Settings > General & Privacy > Terms & Privacy. Turn off Viewing Information Services, which is the ACR toggle, and Interest-Based Advertising. On older Tizen sets the same options sit under Support > Terms & Privacy. Decline anything offered during setup, too — those consent screens are where most of this gets agreed.

LG

Go to Settings > All Settings > General > Live Plus and switch it off. Live Plus is LG's ACR service. Then look in General > System > Additional Settings for advertising or interest-based ad options, and turn off any content recommendation service you find in the same area.

Roku, and Roku-based TCL and Hisense sets

Under Settings > Privacy, open Smart TV Experience and untick the option to use information from TV inputs. That is the ACR switch, and it covers terrestrial channels and HDMI devices as well as streaming apps. In the same menu, set Limit ad tracking on. Roku will warn that some features stop working; that is the trade.

Amazon Fire TV

Head to Settings > Preferences > Privacy Settings and switch off Device Usage Data, Collect App Usage Data and Interest-Based Ads. If nobody in the house uses voice search, disable Alexa on the device from the same area — otherwise every stray word near the remote has a route to a server.

Google TV and Android TV

In Settings > Privacy, turn off Usage & Diagnostics. Then open the Ads section and delete the advertising ID, which stops apps linking activity to your set. On Google TV, also turn off personalised recommendations if you would rather see a neutral home screen.

Apple TV

Apple does not run an ACR programme, so there is less to disable. In Settings > General > Privacy, turn off Share Analytics, and check the TV app's own settings for anything labelled with your viewing history.

Voice assistants and microphone data

Voice commands are sent to a server to be transcribed, and the recordings are often kept. Where a set offers a voice recognition toggle, switch it off and use the on-screen keyboard instead. If you do want voice search, look for the auto-delete option in your account — Amazon, for instance, lets you set Alexa recordings to be erased automatically after a short period, and lets you review and delete individual clips.

Worth knowing: a remote with a microphone button is usually only listening when you press it, unless the set also has a hands-free wake word. If yours does, treat that toggle as the one to check first.

Blocking the traffic at the router

Settings can be reset by a firmware update, and some tracking happens at app level rather than in the TV's own menus. Blocking outbound requests is the belt-and-braces approach.

1. Find the set's MAC address in its network or about screen, and note it down.
2. Reserve a fixed IP address for the TV in your router's DHCP settings, so any rule you write stays attached to the right device.
3. Point the network at a filtering DNS resolver. Pi-hole on a spare Raspberry Pi, NextDNS or a similar service will let you block telemetry and ACR hostnames across every device at once, with a query log you can actually read.
4. Block outbound DNS from the TV on port 53. Some sets ignore the resolver your router hands out and call home directly.
5. Cut the set off entirely if you do not use its built-in apps. Deny it internet access, or drop it on a guest network with no onward route. Streaming then happens through a separate player you have configured yourself.
6. Read the logs after a week. You will see exactly which domains the set tries to reach, and you can decide case by case whether to allow them.

One caution: aggressive blocking can break things. A blocked domain might be serving programme artwork or an electronic programme guide rather than a profile. Add rules one at a time so you know what caused the problem.

The option nobody mentions: don't connect it at all

A television that has never joined your wi-fi cannot report anything. Set it up without a network connection if the menu allows, then feed it through an HDMI stick or a small media PC that you control and update yourself. This also keeps the TV's software out of the loop when the manufacturer stops issuing security patches — a real concern once a set is a few years old.

Remember that tracking then moves to the streaming device, so go through its privacy settings too, and turn off watch history in the apps you use most. Netflix, YouTube and the BBC all keep viewing records tied to your account, separate from anything the television is doing.

A short routine to keep it off

Check your TV's privacy settings again after every major update, because they occasionally reappear. Resetting the advertising ID every few months limits how long a profile can be stitched together. And treat the phrase "recommended for you" as a prompt: recommendations need a profile, and a profile needs data you probably did not mean to give away. Ten minutes now, a quick annual audit, and your viewing habits go back to being your own business.

Photo: renateko / Pixabay