> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vouch.expert/llms.txt
> Use this file to discover all available pages before exploring further.

# Device Fingerprinting

> Advanced fraud detection through device tracking

## Overview

Device fingerprinting creates a unique identifier for each device accessing your application, allowing you to track the same device across multiple signups and detect multi-accounting.

<Note>
  Fingerprints are automatically collected by client SDKs. Server-side SDKs receive fingerprints from the client.
</Note>

## API Response

```json theme={null}
{
  "checks": {
    "device": {
      "pass": true,
      "latency": 12.5
    }
  },
  "metadata": {
    "fingerprintHash": "abc123def456",
    "previousSignups": 0
  }
}
```

When device reuse is detected:

```json theme={null}
{
  "checks": {
    "device": {
      "pass": false,
      "latency": 15.2
    }
  },
  "metadata": {
    "fingerprintHash": "abc123def456",
    "previousSignups": 3
  },
  "signals": ["device_reuse", "device_seen_3_times"]
}
```

<ParamField path="pass" type="boolean">
  `false` if device has been used for 3+ signups, `true` otherwise
</ParamField>

<ParamField path="latency" type="number">
  Check execution time in milliseconds
</ParamField>

<ParamField path="metadata.fingerprintHash" type="string">
  Unique device fingerprint hash
</ParamField>

<ParamField path="metadata.previousSignups" type="number">
  Number of previous signups from this device
</ParamField>

## Configuration

<Card title="FLAG" icon="flag" color="#f59e0b">
  Recommended to FLAG device reuse since multiple accounts may be legitimate (family devices).
</Card>

## Next Steps

<CardGroup cols={2}>
  <Card title="IP Reputation" icon="shield-halved" href="/validation/ip-reputation">
    Detect VPNs and fraud
  </Card>

  <Card title="Alias Detection" icon="at" href="/validation/alias">
    Detect email aliases
  </Card>
</CardGroup>