How AI voice agents tell a live person from a voicemail

Voicemail detection, also called answering machine detection, decides within roughly three to five seconds whether an outbound call reached a live person or a recording, relying on timing and behavior signals rather than voice audio. A 2026 arXiv preprint found timing features alone can match beep- and keyword-based approaches while avoiding their added latency. Vapi lets users choose a detection provider, tune timing, and switch back to conversation when a human answers.