Check Six Rearview Sunglasses

Sunglasses with a mirrored strip on the outer edge of each lens. Look straight ahead and you see what is in front. Glance to the edge and you see what is behind you, without turning your head.

For queues, train platforms, crowded streets, or anywhere you would rather know who is behind you without making it obvious. "Check six" is pilot talk for watching your back.

The specs: matte black plastic frame, TAC lenses with UV400 protection, filter category 3 (standard sunglasses for bright days), non-polarised. Lens 62 mm wide x 35 mm high. One size, unisex.

What it does not do: the rear view is a narrow strip, not a full mirror, and it takes a few minutes to get used to. It works best in daylight. Category 3 lenses are too dark for driving at night or at dusk. It does not block any electronic tracking: it just helps you see who is behind you.