Question

How accurate is answering machine detection?

Applies To

• Voice API
• Answering Machine Detection

Answer

We use a Call Progress Analyzer (CPA) for answering machine (voicemail) detection. While there is no consistent signaling difference between a call picked up by a human or a machine, we detect voicemail using data from the tone of voice and the speed of words spoken. This detection usually takes 3 to 5 seconds. Vonage's machine detection typically has an accuracy on par with industry standards, where 60% to 80% of calls can detect an answer machine correctly.

If a machine is detected during this time and machine_detection is set to hangup, the call hangs up immediately and the status parameter value sent back to your webhook URL will be set to machine.

Machine detection for Google Voice numbers is not supported due to the short greeting on the initial answer of the voicemail. Due to the length of the message, this is recognized as being answered by a person and so the call will continue.