Privacy screen protectors, and what the filter costs you in brightness

A privacy screen protector is one of the few phone accessories that does something you can see, and the thing it does is a trade. Twenty of them are on this page, nineteen with a privacy filter, and the titles are enthusiastic about pack sizes and generation lists and silent about the trade.

How a privacy filter works, and what it costs

Inside a privacy protector is a layer of microscopic louvres, like a very fine venetian blind stood on its edge. Look straight through and it is almost clear. Tilt past about thirty degrees and the louvres line up and the screen goes black. That is the whole feature, and it works: the person in the next seat sees nothing.

What no title here says is that you are looking through the same blind. Straight on, the louvres still take a slice off the brightness, and the screen looks a shade darker and cooler than it did. Most people turn the brightness up to compensate, and the battery pays for that all day. Tilt the phone to show someone a photo and they see the black screen you bought it for.

If you read on a train or type passwords in public, that is a trade worth making. If you mostly use the phone at home, a plain protector is the same glass without the tax.

One title says four-way, meaning the louvres run both ways and the screen blacks out from above and below as well as from the sides. On a phone held upright in a queue, above is where the eyes are.

Glass, ceramic or hydrogel

Sixteen titles say tempered glass. It is hard, it feels like the screen underneath, and when it takes a bad knock it cracks so the screen does not. That is what it is for.

Three say ceramic, and the word is doing some work. A ceramic protector is a flexible plastic film with a hard coating, sold on the fact that it will not shatter. It will not, and it scratches more easily than glass and feels slightly soft under a nail. It is the right choice for a phone that gets dropped a lot and the wrong one for a pocket with keys in it.

One is hydrogel, a soft TPU film that is cut to hug a curved edge and heals small scratches over a day or two. It is the quietest of the three to live with and the easiest to mark.

The words that mean nothing

9H is on one title. It is a pencil hardness: the hardest pencil that drags across the surface without scratching. Every tempered glass protector on sale passes it, and so does most ceramic film. It separates nothing.

9D, on another, is not a hardness. Sellers use 2.5D, 3D, 5D, 9D and 11D for the shape of the glass’s edge, and the number goes up because the last seller’s did. Read it as full cover with a curved edge, and check whether that suits your case.

8K, on one title, is a screen resolution and has no meaning on a sheet of glass.

Matte

Four titles say matte. A matte protector has a frosted surface that kills reflections and fingerprints and gives a finger a paper-like drag. It also softens text, a little, the way a frosted window does, and it is worth knowing that a matte privacy protector is two darkenings at once. Outdoors, in sun, it is the best of these. In bed, at night, it is the worst.

The fitting, which is where protectors fail

Five titles say dust free, easy install or come with an alignment frame. That is the part to care about. A protector goes on badly because of a hair, a speck, or a hand that puts it down two millimetres left, and a frame that sits over the phone and drops the glass in place removes all three. A protector without one is the same glass with a coin-flip fitting.

Two titles say oleophobic, one of them spelt wrong. That is the coating that makes a finger slide and a fingerprint wipe off, and it is on the factory screen you are covering. A protector without it feels sticky and smears. Only two of twenty mention it, and the rest may or may not have it.

The model list

Every iPhone title here is a list. One runs from the iPhone 6 to the 18 Pro Max. You choose the actual size from a menu at checkout, and a privacy glass cut for a 15 Pro is a millimetre wrong on a 16, which is enough to lift at the edge.

Find the model number in Settings, then choose. Do not choose by the year you bought it, and do not trust the photograph, which is of whichever phone the seller had.

Full cover, on three titles, means the glass goes to the edge. Some cases have a lip that catches a full-cover edge and lifts it within a week. The MagSafe case guide covers what to look for in the case; here, if you use a case with a lip, half cover is the safer choice and the titles will not tell you which they are.

What none of them says

Thickness. Not one title. Tempered glass protectors run from about 0.2 to 0.4 millimetres, and the thin ones fit under more cases and crack sooner.

Whether Face ID and the front camera are cut correctly. No title mentions the cut-out at all, on a product where the cut-out is the part that can go wrong.

How much light it blocks. None. The honest ones say around a quarter.

What I would actually do

For most people, the Joyroom. It is the one maker’s name on the page, and a name is a size chart and a customer service address.

For the fitting, the one that says oleophobic and comes with a frame. The coating is the difference between glass you notice and glass you do not, and the frame is the difference between one attempt and three.

For a commute, the four-way. It is the only title that blocks the direction a standing stranger looks from.

If you hate reflections, the matte one with the frame, bought knowing you have chosen two darkenings and the sun will thank you for both.

Whichever you choose, know your model number first, and expect to turn the brightness up.