Voicemail Detection

Voicemail Detection: Providers and Configuration

Overview

Sulus provides flexible voicemail detection for outbound voice agents, allowing you to choose from multiple detection providers and fine-tune their behavior.

Detection Providers

You can choose between several detection methods:

Detection Method	Strengths	Weaknesses	Recommendation
Sulus	Fast, accurate, gracefully handles interruptions	None significant	Strongly recommended
Google	Very good accuracy, reliable	Slightly longer detection time than Sulus	Recommended
OpenAI	High accuracy, flexible phrasing	Higher cost	Good option if budget allows
Legacy Carrier Beep Detection	Very fast machine beep detection	Prone to false positives	Use only in special cases
Sulus Voicemail Tool (beta)	Assistant-driven voicemail decisions, most cost effective	Requires good prompting	Best for customization and cost efficiency

How Sulus Detection Works

Sulus's detection engine uses a hybrid approach combining:

Gemini model-based detection, fast and highly accurate on common voicemail phrasing
Carrier-level beep detection, optional, for faster reaction to voicemail system beeps
Real-time call monitoring, reacts instantly if a human unexpectedly picks up
Continuous voicemail polling, detects voicemail faster without waiting for a full timeout

All three providers, Sulus, Google, and OpenAI, support interruption handling and false positive protection.

Advanced Configuration Parameters

Each detection method supports the following parameters:

Parameter	Description
type	Detection method: audio (default) or transcript (ASR-based). Only transcript is supported for Google and OpenAI providers.
backoffPlan.startAtSeconds	How long to wait before starting voicemail detection.
backoffPlan.frequencySeconds	How frequently to check for voicemail (minimum: 2.5 seconds).
backoffPlan.maxRetries	Maximum number of detection attempts before stopping.
beepMaxAwaitSeconds	Max time from call start to wait for a voicemail beep before speaking. Default: 30 seconds (range: 0-60).

beepMaxAwaitSeconds: Important Notes

Setting this value too low (under 15-20 seconds) may cause your voicemail message to be cut off, since most voicemail systems play 10-20 seconds of greeting before the beep.

Recommended values:

Conservative: 25-30 seconds (default)
Aggressive: 15-20 seconds (requires testing)

Example Configuration

Here's a basic Sulus provider configuration (recommended):

{
  "voicemailDetection": {
    "provider": "sulus",
    "backoffPlan": {
      "maxRetries": 5,
      "startAtSeconds": 2,
      "frequencySeconds": 2.5
    },
    "beepMaxAwaitSeconds": 30
  },
  "voicemailMessage": "Hi, this is Sarah from TechSolutions. Please call me back at 555-0123. Thanks!"
}

You can also configure this via the Assistants tab in the Sulus dashboard under the Voicemail Detection section.

In summary, Sulus's voicemail detection is highly configurable, supporting multiple providers with fine-grained control over timing, accuracy, and cost. The Sulus provider is strongly recommended for most use cases due to its speed and accuracy, while the Sulus Voicemail Tool (beta) is best for cost-sensitive or highly customized scenarios.

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