Making a privacy monitor from an old LCD

privacy-screen

[dimovi] had a spare LCD monitor sitting around and thought it would be great to convert it into a “privacy” monitor.

The process is simple enough for anyone comfortable with disassembling electronics. He took apart the monitor’s plastic frame, cutting out the polarized film with a utility knife. Once the film was removed, he spent some time removing the film adhesive from the glass panel using a combination of Oops cleaner and paint thinner.

He reassembled the monitor, which now shines a bright white regardless of what is actually being displayed on the screen. He removed the lenses from a pair of theater 3D glasses, replacing the plastic with the film he removed from the monitor.

Now, [dimovi] is the only one who can see what’s he is doing on his computer, which is just the way he likes it.

While there’s not a lot of magic going on behind the process, we think it’s a neat way to reuse an old monitor.

91 thoughts on “Making a privacy monitor from an old LCD

  1. What is the chance of using this kind of setup in a laptop at a public place someone thinks that a crazy guy is staring at a white monitor?

    1. Pretty darn easy apparently, as long as you’re ok with ripping apart your laptop’s screen.

      Sweet hack though. I would have never thought of this.

      1. Great idea, until you realize that EVERY PAIR OF CHEAP SUNGLASSES will work on this too. Polarized lenses are pretty standard now.

    1. How about using electronically controlled polarizing material? You could have the screen normally visible to the naked eye, then flip a switch to enable privacy mode.

      I’m amazed on laptop manufacturer has thought of this. IBM/Lenovo used to make a point of using screens that have a very narrow viewing field so that the person sat next to you on the train can’t read what you are working on.

      1. It’s because anyone with polarised glasses would be able to see other peoples screens, ie. Giving them a false sense of security – which is usually worse than no security at all…

      2. IBM/Lenovo used to make a point of using screens that have a very narrow viewing field so that the person sat next to you on the train can’t read what you are working on.

        Good old marketing department. They probably had a batch of less desirable LCD screens they needed to get rid of :)

      3. As much as marketing is typically who we love to blame for coverups in this case it was the higher end business machines only with the extremely narrow viewing angles. So it may actually be a case of building a device marketing wanted, rather than marketing a poor device that was built.

  2. I have an old 15″ lcd sitting right here actually… while this would be a really neat idea, what happens when you lose the glasses/any spare Polaroid film?

    1. Cheapest ways would be to just buy some cheap polarized glasses off ebay that are used for watching 3D movies and re-orienting the lenses. Maybe you could make some glasses out of old camera polarising filters.

      Edwin Land (the founder of the Polaroid company and chief designer and scientist, a true genius) was the first to develop a cheap way of making polarizing filters in large quantities back in the 1930s, he called this product Polaroid film, which the company is named after. The first instant photographic camera and film was released in 1948 for which the name is now come to mean.

      Technically the film used on monitors today is the same stuff Land developed and is called Polaroid film, though i’m fairly certain that’s not what you meant? Since this stuff is produced in vast amounts i can’t imagine it being too hard to acquire some for home use.

      1. But regular “polarized glasses” will work.

        If you go to a new gas pump that has an LCD display, wearing regular polarized glasses, sometimes you can’t see the display, unless you tilt your head 90 degrees.

        That depends on how the two are oriented.

        I run into that problem ALL the time.

        And yep, you can by circular polarized “lens” for cameras (supposedly the circular is best for digital camera) or the older linear, which is supposed to be best for analog film.

        Just have to look at the package (or ask the sals person) when you buy them.

      2. Quick little correction circular vs linear polarization has nothing to do with film vs digital. Linear can do a better job of knocking down reflections, but it can interfere with auto focus and light metering in SLR cameras.

  3. Neat idea. Standard polaroid glasses, at least the ones I have, have the grating angled at 45 degrees so as not to interfere with lcd screens (gps, car dash,..) So if you could rotate the film in the screen 45 degrees, you might be able to use standard polaroids..

    1. The problem is there’s nothing standard about how manufacturers orient the filters on their LCDs. I especially love the two monitors I have at work. Both Dell, but two different models. With my sunnies on I can only see one of them. Tilt 90deg I can only see the other.

  4. Haaaaa.
    I cant think of any reason for doing this at home, save for preventing anyone from seeing you surf porn!
    Although am I correct in thinking that all u need to ‘subvert’ the privacy is to put on an ordinary pair of sunglasses, polarised of course?

  5. actually this monitor can be viewed correctly through any non-metallic reflection since the reflection coefficients for in-plane and perpendicular polarisation directions differ under an odd angle ;-)

  6. Why didn’t I think of that?
    Really cool idea, I though of something like that once when I was outside, I had sunglasses on and my friend passed me his laptop, tilting my head would fade the display. It would be really cool on a laptop that is used for commuting; you could get some work done without worrying too much about prying eyes (although technically it would be the equivalent of putting a door without a lock on a house). Might attempt it on an older unit I have…

  7. In the army and in most hospitals we use add-on polarized film (almost looks like a polarized fresnel lens) to keep prying eyes away from sensitive data. The big difference with the design of our screens, you can only see the screen if you are looking from direct center of the screen. Any angle and you can’t see squat.

    I would love to see this idea for doctors having to check patient records and x-ray/mri while out of the hospital. Maybe in an iPad or some other tablet format…

    Cool stuff!

  8. Great! Using it in public would be awesome. Note that glasses for polarized 3D films would probably be better than polarized sun glasses unless you don’t care about brightness.

    1. Good point. But wouldn’t you need to align the polarization of the glasses in the 3D specs in order to get the same image in both eyes?
      I am not a physicist, but I’d imagine that you’d get differing brightness levels depending on the angle of polarization.

      1. That’s a good point too :) The polarization for 3D film glasses is perpendicular for each eye I believe; you might combine two glasses into a new one for a single direction.

  9. as i remember my previous laptop LCD have glass with pixels as first sheet.
    so be carefull, i would not say that this hack applies to any screen

  10. Don’t a lot of glasses and sunglasses nowadays have polarizing coatings to reduce glare? I swear I saw displays for that in my eye doctor’s office several times over the past ten years.

    1. Nowadays? You have a grand view of history since they’ve been doing it for many decades, polaroid is famous for them and they’ve been around since before you were I bet.

      1. Here’s a surprising thing: Some people can.. and you may want to sit down for this revelation.. learn about things from before their birth *gasp*

        Did I just blow your mind? I hope you are alright.

        Ask me later about a site called wikipedia.

  11. You could make it more secure by having a program to either turn on the monitor or mask the entire screen with white pixels, then oscilate it at a low frequency.

    The glasses would be electronically polarized at the same frequency so it turns on when the monitor is unmasked.

    Sounds good in theroy, but just a thought

    1. I had the same idea, but it wouldn’t be a good solution.

      Why? Because all you’d need is sunglasses where the polarization of the two lenses is 90 degrees to each other. Then you’d see a combination of the screen image at all times (your brain would stitch them together for you).

      1. Hay,

        That will work, but it will have the same effects and problems as the older 3D movies did (which had those heavy glasses that were synced with an infrared light source)

        Besised, like everyone else is saying, you can buy a pair of poloride glasses anywhere these days, and varying the angle wont work since you can just put on normal 3D glasses (with the perpendicular lenses) and one of your eyes WILL see the image, if not just vaguely both of them (if the film is at say 45*)

        Cherz

  12. hey,

    I used a very similar technic for an art project.

    I used a overhead projector to project a “polarized image”. then there is a mirror coated with another polarizing filter and if you look into it you can see a message.

    more details on the project page:

  13. I have got to do this on a laptop (cheap laptop), and mabye if I can score a cheap LCD TV I could do it on that too, and hook it up to DVD player continuously playing “They Live”!

  14. I did this on an old laptop today. Without polarized glasses, you can still barely see the faint outline of white on black, and windows, but can’t see what’s going on inside windows or images.

    Advice:
    – It’s not always that easy to remove the diffuser and the polarizer. Mine are clearly two pieces of plastic, but I don’t think I’m going to be able to separate them. They also were difficult to remove.
    – Avoid bending the LCD glass and avoid getting paint thinner between the LCD and the backlight diffuser. I have some funky cloudy patterns visible now. I would suggest against the paper-towel & paint thinner method, perhaps just IPA & a razor blade would work better.

  15. You can heat the LCD a little bit with a hair dryer on hot, to soften the glue up. I use this trick to remove labels, keeps me from having to use oops or other solvent, or leave nasty glue still on the object.

  16. I hate to spoil this for you all but this hack is useless, who would pick a spyesque tech hack when there’s the privacy sock?

    /s

    1. Haha.

      “that’s an ideal solution” – Pickpocket

      “A solid sound invention” – Convicted womengroper

      “Not bad, not bad at all” – Snarky internettroll

  17. I’m having a little trouble and I hope that someone can help me. I’ve removed the casing from my monitor and peeled a sheet of the 2 films that are stuck together from about 1/4 of the monitor. Now I’m trying to separate them and cannot get them to seperate. I’m terrible at directions, so if someone could give a little more insight I would be very grateful.

    tl;dr: I can’t seperate the 2 films, help me.

  18. I just finished doing this. It is awesome to say the least. I couldn’t get the AG film and polarized film to seperae, so I ended up pulling both off with a paint scraper and paint thinner. I got a pair of polarized sunglasses, and turned them to the left 45* and that works just fine. I’m going to turn them fully tomorrow, and solder them at that angle permanently.

    Thanks for the great hack, dimovi!

  19. I had done this *exact* thing a few years ago when I was working at a big government research lab. At the time we were playing around with layering multiple LCD screens (with and without polarizing filters peeled off) to create a new kind of 3D display. After realizing the front polarizer could be removed to make a privacy monitor, we toyed with commercializing this idea or putting it to use for sensitive information at the lab. However, in the end we determined it is too simple to defeat for any serious purpose. Even if you make sure no one is wearing sunglasses nearby, a hidden camera with a polarizing filter could still record everything on your screen. By the way, regular polarized sunglasses (such as for driving) work just fine — there is no need to make special glasses as in the Instructable.

  20. I had done this *exact* thing a few years ago when I was working at a big government research lab. At the time we were playing around with layering multiple LCD screens (with and without polarizing filters peeled off) to create a new kind of 3D display. After realizing the front polarizer could be removed to make a privacy monitor, we toyed with commercializing this idea or putting it to use for sensitive information at the lab. However, in the end we determined it is too simple to defeat for any serious purpose. Even if you make sure no one is wearing sunglasses nearby, a hidden camera with a polarizing filter could still record everything on your screen. By the way, regular polarized sunglasses (such as for driving) work just fine — there is no need to make special glasses as in the Instructable.

    1. Exactly.. You couldn’t commercialize it as it’s too easy to defeat and any privacy value is inversely proportional to the amount of people who are aware of the tech / have the glasses.

      This is only really useful as a DIY project when a handful of people use it

  21. It’s not just the privacy ! there is another very important effect : the reduction of ambiant light .
    The light coming from the monitor passes 100% BUT the ambiant light is reduced by 50% .
    You can do a simple experiment to see this effect : look at a polarized filter through another polariser filter you will see the polarirized filter ABSOLUTELY transparent like glass ( the polarized filter is grey in fact ) . This is due to the reduction of ambiant light by 50% while the light coming from the polarizer passes 100% inchanged .
    It is useful in outdoors where the sunlight will be cut by 50% while not impacting the light coming from the monitor .
    I have proposed this idea many years ago to a researcher but he was not interested in , but perhaps the people here who commented this post can give it a try !

  22. Its a shame because I did this on my computer monitor and the screen isn’t in focus unless the film is within six inches of it.

    1. You still have the anti-glare on there. Your monitor probably has them glued together too closely to peel. I would suggest just buying/using polarized sunglasses instead of making your own.

  23. Now I can disguise my monitor as a lightbox and pretend I’m meditating or doing light therapy. Maybe combine it with a Kinect, and people will think I’m the Zen master, staring into a white rectangle and making strange movements.

    Where do I get polarized contact lenses?

  24. For the average geek, being the only one able to see what is the monitor is not the problem, rather the average geek have the reverse problem. That is finding someone else to watch the monitor with.

  25. This is so fake it’s absurd. Tell us how the information about what is on the screen is relayed to the glasses? Considering that a monitor is merely a liquid crystal display in front of some backlighting. How does tyhe liquid crystal display get the info on what is displayed on the screen after it is removed and cut up? I call bullshit.

    1. It’s not fake it is real !
      Your questions are legitime . I understand that it seems to you extraordinary but if you do some simple experiments with polirizing filters you will be amazed ! For example you can put a polarizing filter on top of another one so that they appear completly black and when you insert a third polarizing filter between the two the light can go through the three layers !!! .
      You can have polarizing filter from an old lcd display (from an old calculator) and explore all the possibilities .

      1. That has to be the most ridiculous thing I have ever heard – “put another filter between them, and see through all 3″… that’s not how they work genius…lol.

  26. I’m imagining this hack could be used to turn regular LCDs into 3d displays with perpendicular polarized glasses and an appropriate display driver.
    But I think the fact that polarization is used to change pixel brightness will get in the way.

    Maybe a tradeoff between quality and 3d feature?

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