Porn blockers: how they work and what to look for

The four layers

It helps to think about where a block can happen, because most products only operate in one place and the gaps are predictable.

• Network.Known destinations are stopped before they load, for every app on the device. Fast and cheap, but only as good as the list.
• Content.What actually arrived is inspected on the device, so a domain registered this morning is caught the same as a known one.
• Screen.On-device models flag explicit imagery by what is displayed, whatever app put it there. On the phone it is optional, because reading the screen costs battery and sees everything.
• Cool-down.A delay on loosening a rule, allowing a site, or removing the app. This is the layer that decides whether the other three survive.

Why the cool-down is the whole argument

Every blocker can stop a website. The question is what happens at the moment you want it to stop stopping you, because that is the only moment that has ever mattered.

If the answer is "you switch it off", the product is decoration. If the answer is "you make a request and it waits", you have a commitment device, and the urge is almost always gone before the timer is.

Reporting tools are a different product

Accountability software detects what you looked at and tells someone about it. Covenant Eyes pairs that with website filtering, so it does block the sites it recognises. What the model does not do is judge a page nobody has classified, and that page still loads.

The question to ask yourself is whether you want the content stopped or the behaviour reported. They are different jobs and the tools are built differently as a result.

What to check before you pay for one

• Can you switch it off instantly?If yes, it will not hold.
• Does uninstalling take two clicks?Then so does defeating it.
• Is it browser-only?Your other browser is already installed.
• Does it cover your phone?That is where most of it happens.
• Who else can read your history?Detection should run locally, and whatever it records should be readable by you and nobody else unless you decide otherwise.