A Button To Hide Your Secrets
We all have something we'd rather keep to ourselves. Maybe it's a weakness for inspirational quotes on driftwood. Maybe it's a Tiramisu habit that sits awkwardly nestled among your probiotic activated charcoal smoothies. Maybe (and we're not judging, this is a safe space) it's a decades-long, fully-shrined devotion to a young David Essex.
Whatever it is, you deserve to enjoy it in peace.
This project is a wireless panic button that turns a sheet of glass instantly frosted. No wires, no batteries, and no questions asked. You can build one yourself for about thirty euros. Or win ours (more on that below).
How It Works: The Science Bit
The magic ingredient is smart glass, properly called PDLC film (Polymer-Dispersed Liquid Crystal film). It sounds expensive. It isn't.
The film is a sandwich: two thin, transparent sheets that carry electricity, with a special plastic layer in between. That plastic layer is stuffed with millions of microscopic droplets, and inside each droplet are countless rod-shaped molecules. These molecules are liquid crystals: they can flow like a liquid, but they also have the ability to line up in an orderly way, almost like a solid. This dual nature is what makes them so useful.
Power OFF: With no electricity running through the film, the liquid crystal molecules inside each droplet point in random directions. Light hits a droplet, can't find a clear path through, and scatters. The window goes frosted. Privacy achieved.
The droplets are only a few micrometres across, just a few times bigger than the wavelength of visible light, which puts them in exactly the right size range to scatter light efficiently. This is called Mie scattering (pronounced "MEE", like you're agreeing in a very small voice). You've seen this effect before: when you pour ouzo into water, microscopic oil droplets form instantly and the whole thing goes cloudy. Same physics, slightly fewer secrets.
Power ON: Apply a voltage and an electric field snaps all the liquid crystal molecules into alignment. They all point the same way, light passes straight through without bending, and the glass goes clear. It's similar to how a piece of clear ice can almost disappear when you drop it in water: when the refractive indices match up, things become transparent.
The switch between these two states is essentially instant. One click and the glass flips. Which makes it oddly satisfying to use.
The Build
What You'll Need
- Some private stuff (use your imagination)
- PDLC film
- Something transparent to stick it on (we used glass, but acrylic works too)
- A wireless switch, ideally one that runs without a battery
- 3D-printed feet for the screen
- A 60V AC power supply
- A 100 kΞ© bleed resistor
Three Steps
1. Apply the film. The PDLC film goes onto your glass or acrylic panel. Take your time here: bubbles are the enemy. Clean the surface well before you start.
2. Wire the switch. Wire the PDLC film in parallel with a 100 kΞ© bleed resistor on the 60V AC supply. The resistor's job is to safely drain any residual charge from the film when the power is switched off. Without it, the glass can stay partially clear for a moment after you cut the power. Not ideal when you're in a hurry to hide things.
3. Seal the connections. 60V AC can cause a mild shock under the wrong conditions, so all live connections (including the bleed resistor) go inside a small enclosure. No live parts should be exposed. This is the unglamorous part of the build, but do it properly.
The 3D-printable files and a full parts list are in our GitHub repository.
What Might You Be Hiding?
We tested a few scenarios during filming.
A fondness for fruit and a fondness for Tiramisu aren't necessarily contradictory, but they're easier to manage separately. The smart glass helps.
A love of books is a respectable thing. A love of motivational phrases stencilled onto driftwood is perhaps more of an acquired taste. No judgement. The glass handles this too.
And then there's the shrine. A carefully curated, lovingly assembled tribute to a young David Essex in the full glory of his Rock On era. A man with a glint in his eye and a narrowboat between his legs. The glass was practically designed for this.
Win This One (EDIT: Someone won it)
Behind the privacy screen in the video is a mystery object. We're not going to tell you what it is, and we've taken steps to make sure AI can't just figure it out from context clues.
To enter: guess what's behind the screen and leave your answer in the comments.
One correct answer will be picked at the end of October 2025, and we'll get in touch to arrange delivery.
Good luck. And remember: everyone has something worth hiding.
Inspired by those Innovations catalogues that used to fall out of the weekend UK newspapers. RIP to a fine publication.
