CallDrop

CallDrop is an in-line device that works by presenting the robocaller with an immediate disconnect triple tone before briefly pausing and asking the caller to dial an additional passcode number (1 to 3 digits long, randomly generated) to complete the call. It is therefore theoretically impossible for a modern robocaller to bypass both the triple-tone disconnect, and the passcode. Essentially, the passcode serves as a form of Turing Test, and works like a modified Private Branch Exchange (PBX).