14" and Under

A privacy filter blacks out the screen to anyone looking from either side, which is exactly what a laptop needs on a train, in a café, in an airport lounge or in an open-plan office. For anyone handling personal data, client information or financial records away from a desk, it is a basic precaution rather than a luxury.

Measuring. The stated size is the diagonal of the visible screen, and it must be paired with the right aspect ratio — 16:9, 16:10 and 3:2 filters of the same nominal size are different shapes and do not interchange. Many business laptops and Surface devices use 16:10 or 3:2, so check rather than assume.

Attachment. Adhesive tabs and side slots hold frameless filters; magnetic versions attach and detach in seconds, which is worth the premium if you only need privacy some of the time.

Touchscreens need a filter rated as touch-enabled — a standard one will interfere with touch response.

Most filters also reduce glare, a useful side effect on a bright train.

The range covers Fellowes, Kensington, StarTech, Targus, HYPER and PREVO.