Years ago someone made a script where Asterisk would answer immediately with a short burst of number unavailable tone - too short for a human to hang up, but lo

Years ago someone made a script where Asterisk would answer immediately with a short burst of number unavailable tone - too short for a human to hang up, but long enough for robo caller to detect and hopefully take off it's active numbers list, in the hope of reducing automated calls... not sure if it's still around, or if the robocallers got wise to it.