How to stop Robo-calls

This is what i have done in the past to stop Robo-callers. When i see a phone number on my caller ID that i know is a Robo-caller I answer the phone with the Special Information Tone(SIT) for Reorder – interLATA, which is the three tones for Call failure, no wink or partial digits received – distant office. These SIT's are found in Wiki. Since Robo-calls are computers that listen for these tones, a small device such as a Tone-generator will work and can be kept on a key-chain. This is will be a hand held device that stores telephone numbers and SIT's and when placed up to the reciever it would play the tones for any stored phone number in it's memory or the three tones for "Call Failure".