People buy dma cards and displayport/hdmi mergers to avoid hack detection. Another pc reads memory of your gaming machine through the dma card that creates your ESP overlay and then dp/hdmi is merged through a box. The dma card runs custom firmware that pretends to be some benign peripheral like an usb or soundcard.
There's also hardware aimbot/triggerbot that reads your video output then sends input to a device connected to your mouse.
Its not what your everyday cheater has in free to play games like cs or cod but there are games where it matters more if you're banned, and when cheat subscriptions can be $100-200 a month the hardware cost isn't much.