SpyShield Screen Protector

Available on the market are screen protectors that limit the viewing angle of your laptop, smartphone or tablet's screen, which, of course, would be a very handy physical security/privacy solution when working in a public space. I have bought the upscreen Spy Shield Clear for several of my devices, which costed just under £40. The vendor also has screens for a very large range of smartphones and laptops, which cost under £10.

One side of the Spy Shield screen protector is coated with pretty strong adhesive, much stronger than what you get with the average phone screen protector. Of course, it's tricky to remove and refix if you get air bubbles, but it means it's not coming off accidentally. I managed to get the screen attached properly after several attempts without damaging the screen or weakening the adhesive.
In the mounting kit, there are alignment stickers for aligning things, a microfibre cloth and alcohol wipe for making sure the surface is totally clean, and a plastic card for smoothing out bubbles as the screen's applied.

To get the best results from the Spy Shield, I recommend setting a dark colour scheme for your applications, and reducing the screen's brightness as much as possible. This is highly effective in an environment with a lot of ambient light.
Effectiveness varies in other cases - if the screen brightness is set to 80% - 100% in lower light conditions, the screen is still visible from even 90% angle. I noticed the faint lines running through the material also has the effect of making whatever text might be displayed unreadable outside an angle of about 30 degrees.