--- title: Answering Machine Detection (AMD) slug: voice-apis/answering-machine-detection-amd docTags: createdAt: 2026-06-15T09:31:52.042Z --- **Status:** Beta. Please reach out to your Exotel account manager to have AMD enabled on your account. ### Overview Answering Machine Detection (AMD) tells you whether an outbound call was answered by a **human** or by a **machine** (such as voicemail or an IVR). This lets you take different actions depending on who picked up — for example, playing a message only when a human answers, or skipping voicemail drops. AMD results are delivered through Exotel's call callbacks (APIs). They are **not** shown in reports or the dashboard. ### How AMD works When AMD is enabled, Exotel analyzes the audio at the start of the call — the greeting and the silences around it — to classify who answered. The classification is returned through two new parameters inside the Legs object of your callback payload: | **Parameter** | **Description** | | ------------- | -------------------------------------------------------------------------------------------------------------------------------------- | | AnsweredBy | The AMD result. Use this for your final classification. | | AmdCause | The reason behind the result, including the values used for detection. Use this for debugging or understanding why a result was given. | Possible AnsweredBy values - HUMAN — the call was answered by a person - MACHINE — the call was answered by a machine (voicemail, IVR, etc.) - NOTSURE — detection could not reach a definitive result - NA — AMD was not applicable for this leg ### Key behaviors **1. AMD applies only to Leg 2 (the To leg).** Detection runs only on the number being dialled (Leg 2 / the To leg). Leg 1 (the From leg) will always return AnsweredBy: NA. When reading the payload, use the AnsweredBy value on Leg 2 for the human-vs-machine result. **2. AMD detection is asynchronous.** Detection does not block or delay call connection or routing — the call proceeds normally while analysis happens in the background. Because detection listens to the greeting and surrounding silence, the result takes roughly **3–5 seconds** to finalize and is delivered once complete. Consume the result from the callback payload when it arrives, rather than expecting it the instant the call is answered. ### Where you receive the result **A. StatusCallback terminal event** To receive the AMD status via StatusCallback, you must **subscribe to terminal events**. Once subscribed, the AMD result is included in the terminal StatusCallback payload, inside the Legs object. **Sample terminal StatusCallback payload:** :::BlockQuote \{ "CallSid": "f3dec10279a310e2831754a4ec841a5f", "ConversationDuration": "13", "DateCreated": "2026-05-15 16:46:13", "DateUpdated": "2026-05-15 16:46:50", "DetailedStatus": "NA", "DetailedStatusSubBucket": "NA", "Direction": "outbound-api", "DisconnectedBy": "Callee", "EndTime": "2026-05-15 16:46:50", "EventTime": "2026-05-15 16:46:50", "EventType": "terminal", "From": "08203612779", "Legs": \[ \{ "OnCallDuration": "26", "RingingDuration": "5", "Status": "completed", "AnsweredBy": "NA", "AmdCause": "" }, \{ "OnCallDuration": "13", "RingingDuration": "4", "Status": "completed", "AnsweredBy": "HUMAN", "AmdCause": "HUMAN-080-880" } ], "PhoneNumberSid": "8224778996", "RecordingUrl": "https\://recordings.us3.qaexotel.com/exotelrecordings/ree5e1us3/f3dec10279a310...", "StartTime": "2026-05-15 16:46:13", "Status": "completed", "To": "08969916092" } ::: In this example: - Legs\[0].AnsweredBy: NA → AMD was not applicable for the From leg (Leg 1). - Legs\[1].AnsweredBy: HUMAN → the To number (Leg 2) was answered by a human. **B. Passthru payload** When AMD is enabled, the Passthru payload also includes AnsweredBy and AmdCause inside the Legs object. **Sample Passthru payload:** :::BlockQuote \{ "CallSid": "afc75285632df2acd33b7ea1fecb1a4h", "CallFrom": "06203612779", "CallTo": "02247789996", "Direction": "outbound-dial", "DialCallDuration": 27, "DialCallStatus": "completed", "StartTime": "2026-04-17 19:02:06", "CurrentTime": "2026-04-17 19:02:38", "Legs": \[ \{ "Number": "06355212721", "Type": "single", "OnCallDuration": 18, "CauseCode": "NORMAL\_CLEARING", "AnsweredBy": "HUMAN", "AmdCause": "HUMAN-800-800" } ] } ::: In this example: - AnsweredBy: HUMAN → the call was detected as answered by a human. - AmdCause: HUMAN-800-800 → a short greeting was detected, followed by silence — typical human behavior, where the person says "Hello?" and waits for a response. ### AMD Cause reference Use AnsweredBy for your final classification, and AmdCause to understand why that classification was made. Values shown in \{curly braces} are the actual measured/threshold figures used during detection. | **AnsweredBy** | **AmdCause** | **What it means** | | -------------- | ---------------------------------------------------------- | ----------------------------------------------------------------------------------------------------- | | MACHINE | INITIALSILENCE-{detected}-{threshold} | Long silence before any voice started. Machines often have a delay or beep before the greeting plays. | | MACHINE | MAXWORDS-{wordsDetected}-{maxAllowed} | Too many words were spoken in the greeting. Machines usually have longer greetings. | | MACHINE | LONGGREETING-{voiceDuration}-{greetingLimit} | The total voice duration of the greeting was too long. | | MACHINE | MAXWORDLENGTH-{consecutiveVoiceDuration} | A single continuous stretch of voice without a pause was too long. | | HUMAN | HUMAN-{silenceDuration}-{afterGreetingThreshold} | A short greeting was spoken, followed by silence. | | NOTSURE | TOOLONG-{totalTime} | The analysis window ended before a definitive result could be detected. | | NOTSURE | NOAUDIODATA-{totalTime} | No audio frames were received during the analysis window. | | | | | ### Accuracy Exotel detects voicemail using heuristic algorithms based on maximum words spoken, silence, and greeting length. Detection typically takes **3–5 seconds**, with an accuracy of **60–75%**, which is on par with industry standards. There is no consistent signaling difference between a call picked up by a human and one picked up by a machine, so detection relies on audio cues such as tone of voice and speed of words spoken. ### FAQ **Q: A call went to voicemail. Will its status change to "no-answer," or stay in the success bucket?** It stays in the success bucket. The call was successfully connected and answered (by a machine), and these are billable seconds, so the call is not moved to a non-successful state. Use the AnsweredBy parameter separately to determine whether the answer was a human or a machine. **Q: Will the AMD result appear in my reports or dashboard?** No. AMD results are available only through the API callbacks (StatusCallback terminal event and Passthru payload), not in reports or the dashboard. **Q: Which leg does AMD apply to?** Only Leg 2 (the To leg). Leg 1 (the From leg) always returns AnsweredBy: NA. **Q: Is AMD real-time? Will it delay my call?** No delay. AMD is asynchronous — the call connects and proceeds normally while detection runs in the background. The result is delivered through the callback once detection completes (roughly 3–5 seconds).