Droidcam

Droidcam is a mobile app (Android, iOS). With Droidcam the mobile device can be used as webcam for a PC.

Using it as a virtual camera with OBS Studio

Its possible to use Droidcam as a virtual camera in OBS Studio with the following NixOS configuration:

{ pkgs, ... }:

{
  programs.obs-studio = {
    enable = true;
    enableVirtualCamera = true;
    plugins = with pkgs.obs-studio-plugins; [
      droidcam-obs
    ];
  };
}

Since this adds a kernel module, you will need to reboot your system. Once rebooted, open OBS Studio and add a DroidCam OBS source to a scene. Then activate the virtual camera to and make sure it is linked to your selected scene.