26 Layers of Silence.
Zero Data Collected.
Every feature in Callro is built with a single objective: intercept the call before the phone rings, using only the hardware in your pocket. No cloud required. No contact uploads. No exceptions.
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The 26-Layer Gauntlet Engine
When an unknown number calls, Callro's Gauntlet Engine executes 26 distinct heuristics in ~18ms to determine the call's legitimacy. If the score crosses the threshold, the call is terminated.
Protocol Layer (1-8)
- STIR/SHAKEN Attestation Validation
- SIP Header Analysis
- Carrier Registration Verification
- TDM Network Boundary Detection
- Originating Gateway Authentication
- Caller ID Spoofing Signatures
- Unallocated Block Detection
- Invalid Area Code Rejection
Behavioral Layer (9-16)
- Rapid Successive Dialing Patterns
- Neighbor Spoofing Distance Matching
- High-Frequency Originator Checks
- Time-of-Day Anomaly Detection
- Cross-Carrier Burst Patterns
- Sequential Number Generation Detection
- Toll-Free Originator Validation
- Premium Rate Fraud Prevention
Local Layer (17-22)
- Contacts Safelist Match (Offline)
- Recent Outgoing Call Correlation
- Area Code History Profiling
- User Interaction History
- Silent Ringer Pre-Emption
- Fortress Mode Enforcement
Response Layer (23-26)
- SIT Tone Generation (913.8 Hz)
- Database Purge Signaling
- Call Log Sanitization
- Notification Suppression
Permissions Comparison
Cloud-based blockers require extensive device permissions to function. Callro uses Android's native ROLE_CALL_SCREENING API to operate with the absolute minimum privilege.
| Permission | Callro | Truecaller / Hiya |
|---|---|---|
| READ_CONTACTS | Never | Required (Uploaded to cloud) |
| READ_CALL_LOG | Never | Required |
| RECORD_AUDIO | Never | Often Required |
| INTERNET | Optional (For updates) | Required (Always-on) |
| ROLE_CALL_SCREENING | Required (Core) | Varies |
Frequently Asked Questions
What is the 26-layer Gauntlet Engine?
The Gauntlet Engine is Callro's proprietary on-device call analysis system. It runs 26 independent verification checks — including STIR/SHAKEN attestation, number frequency, and behavioral matching — to determine if a call is legitimate in approximately 18ms.
Does Callro need internet access to work?
No. Because the Gauntlet Engine runs entirely on your device, Callro can screen and block calls even when you are offline or in airplane mode with Wi-Fi disabled.
What is Fortress Mode?
Fortress Mode is a Callro setting that restricts incoming calls exclusively to saved contacts. All calls from unsaved numbers are silently intercepted before the phone rings.
How does Callro remove numbers from spam lists?
When Callro intercepts a confirmed robocall, it silently answers and generates a Special Information Tone (SIT). Automated dialers interpret this tone as a disconnected number and purge it from their databases.
Will Callro drain my battery?
No. Callro only activates when an incoming call is received, running its ~18ms analysis and returning to a dormant state. The battery impact is statistically indistinguishable from zero.
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