We display fullscreen data in a projector whose source is the secondary monitor. Sometimes the picture of the projector cannot be viewed by the operator of the computer so we need a control window on the main monitor where we can see what the projector display.

Is there such a program? Something like the little live preview in the Windows taskbar, when you hover over a program, or the magnifier app that you can dock and place the cursor in the second screen.

Only requirement is that is should be free.

2 Answers 2


You could use RealVNC, using the same computer as both the host and the client, specifying in the options to mirror only the projector's display. Assuming you're using Windows, look for the DisplayDevice parameter under VNC server properties

  • Open VNC Server Options
  • Navigate to the Expert tab
  • Select DisplayDevice

The display syntax is as below:


This may or may not be your primary monitor. In a standard right-ordered monitor configuration, they should be ordered Display1, Display2, Display3 and so on. However, to confirm, check your display enumeration in VNC Server > Information Center > Diagnostics.

It's sort of hackish, but it's a viable work-around.


Open Broadcaster Software

As you can see on the image below you can create scenes and from the many available sources you can add one or more monitor/desktop to this scene so you can observe even multiple monitors through the program, or place this scene on full-screen on another monitor. The cursor is displayed too. For this and the reasons below, this is the perfect solution:

  • Many other advanced options
  • Free
  • Open source
  • Cross-platform

Open Broadcaster Software displaying second monitor

  • 1
    This is a very solid solution. As an addition, since the original poster was using Windows, to do this: (1) install OBS, (2) On Sources, click on "+", (3) select Display Capture, (4) Choose the external monitor. // Note if you are running a video on the external monitor, the video may stop upon opening OBS, but you simply just have to resume the video again.
    – plu
    Commented Sep 20, 2020 at 17:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.