The results are sometimes hilarious. Remarkably, a version of TVGuardian is still on the market, updated to send a mute signal to the television’s infrared remote input. It still relies on the closed caption text in the TV signal being displayed, and “compares those words to it’s database of offensive words and phrases”, indicating the degree of attention to detail of the device’s designers and promoters. It only “works” with composite video sources containing closed captioning text in the vertical blanking interval.
Their original patent: