Startup Idea: Device Lockout App or Extension with Secret Key Activation

Startup idea to create an app or extension that locks out any input into devices unless a secret, multi-key combination is used. Unwanted inputs, such as screen touches or button presses, trigger no response during the lockout state. Despite that, the device must continue running its operations with visuals (e.g., movie) still observable on the screen.

I want someone to produce an extension or app that will lock out any input into devices without a secret key. I have to run my computer sometimes for an hour or two, and if my 4 your old sees it's open and unlocked he will mess this it, the same on my phone. I wish there was something to literally lock out any input, closing the screen, key strokes, power buttons, home buttons, literally nothing happens unless you "hold done these four keys" at the same time. It would be vital that it was still running the drives and operations despite the lockout. As an example if I started a movie, which I do for work (good life), and it is running for the next 90 minutes (playback authentication), I need to lock the device and still see the movie running on the screen. Then I want back in, powpow four keys aty the same time, and powpowpow the computer is back toit.