The BIOS screen exists before any operating system, driver or network - and the capture card still shows it on your phone. Here is exactly why, and what it does not let you do.
Ask someone why their second-screen app cannot show the BIOS and the answer is simple: the app lives inside Windows, and the BIOS exists before Windows. The capture card route has no such problem, and the reason is worth stating precisely: the HDMI port sends a picture from the moment the machine powers on, long before any software runs. The card converts that picture; the phone displays it. Nothing in the chain knows or cares whether an operating system exists.
A PC's graphics output is not created by Windows. From power-on, the firmware itself drives the HDMI port - that is how the manufacturer's logo, the POST messages and the BIOS setup appear before any drive is even read. Windows only takes over the same port later.
So the chain - HDMI out, capture, USB, phone - sits below the operating system entirely. It cannot be broken by a corrupt Windows, a missing driver, a failed update or a forgotten password, because none of those things exist yet at the stage where you are working. This is the single biggest advantage this method holds over every software screen tool.
The working method is a two-device dance, and it is important to be exact about who does what:
Typical jobs this enables anywhere: checking boot order on a headless machine, enabling virtualisation, confirming a new drive is detected, reading a POST error, or selecting a bootable USB to start a repair or install.
First caveat: the phone cannot send keystrokes. This route moves picture in one direction only. If you arrived at a headless machine without a keyboard, the phone shows you the BIOS beautifully - and you still cannot press anything. Carry the small keyboard; the kit-bag page in this series exists because of this exact limitation.
Second caveat: unusual display modes. A few older BIOS screens use low, old-fashioned resolutions and refresh rates. Most capture cards handle the standard modes, but a very cheap card may show a black screen in one specific BIOS while working fine in Windows. If that happens, the card - not the machine - is the suspect; test the same machine on a real monitor before concluding anything.
A habit worth stealing from senior technicians: before changing any BIOS setting, screenshot or photograph the phone feed of the original screens - boot order, SATA mode, Secure Boot state. BIOS menus offer no undo, and a setting changed in the wrong direction can stop a working machine from booting.
Because your display is already a phone, this costs you ten seconds. Those photographs are also perfect evidence to send a colleague or a customer: the exact error, the exact setting, no description needed.
The video enters the boot screens live on the phone display - the clearest proof that no software on the PC is involved.
Watch Full VideoNo. The capture card carries picture from the PC to the phone only - it has no path back for keystrokes or touches. BIOS work is always done with a keyboard connected to the PC itself, while the phone acts as your eyes.
Because that app runs inside the operating system. Before Windows or Linux starts, the app is not running and its connection does not exist. The capture card works below the operating system, on the raw HDMI signal the firmware produces from power-on.
Usually not. Many BIOS screens use a low 4:3-style resolution, and the viewer app stretches it to fill the phone. The picture is complete and readable - just set the aspect option in the app to 4:3 or original if it offers one.