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Introduction
Smart TVs and mobile devices are secretly communicating via ultrasonic beacons—inaudible sound waves that link your viewing habits to your mobile identity. This cross-device tracking technique, part of “surveillance capitalism,” operates without user consent. Here’s how it works and how to defend against it.
Learning Objectives
- Understand how ultrasonic cross-device tracking exploits smart TVs and phones.
- Detect and block ultrasonic beacon transmissions.
- Secure your devices against covert surveillance.
1. How Ultrasonic Beacons Work
Ultrasonic beacons are high-frequency sound waves (18–20 kHz) emitted by apps and smart TVs. These signals are picked up by nearby smartphones, allowing advertisers to track behavior across devices.
Detection Method (Linux/Windows)
Use Audacity to analyze audio output:
Install Audacity (Linux) sudo apt install audacity Windows: Download from https://www.audacityteam.org/
1. Open Audacity and select your microphone.
2. Start recording—look for high-frequency spikes (18–20 kHz).
- If detected, your device is emitting ultrasonic beacons.
2. Disabling Ultrasonic Tracking on Smart TVs
Most smart TVs have hidden tracking features. Disable them:
Samsung/LG TV Hardening
1. Navigate to Settings > Privacy > Advertising.
2. Disable “Interest-Based Ads” and “Viewing Data”.
3. Block telemetry domains via router:
Block Samsung tracking (Linux iptables) sudo iptables -A OUTPUT -d samsungads.com -j DROP
3. Blocking Ultrasonic Beacons on Android/iOS
Prevent apps from listening to ultrasonic signals:
Android (ADB Command)
adb shell pm revoke [package.name] android.permission.RECORD_AUDIO
iOS (Workaround)
Disable microphone access in Settings > Privacy > Microphone.
4. Router-Level Protection
Block beacon-related domains:
Pi-hole blocklist addition echo "||sonic-notify.com^" >> /etc/pihole/blacklist.txt pihole -g
5. Detecting Malicious Apps
Use Exodus Privacy (Android) to scan for trackers:
Install via F-Droid adb install fdroid.apk
Check for SilverPush or Lisnr SDKs—common ultrasonic trackers.
What Undercode Say
- Key Takeaway 1: Ultrasonic tracking is pervasive and often undetectable without technical intervention.
- Key Takeaway 2: Proactive device hardening (TVs, phones, routers) is critical to stopping covert surveillance.
Analysis: This surveillance method highlights the erosion of privacy in IoT ecosystems. As advertisers refine cross-device tracking, legislative and technical countermeasures must evolve.
Prediction
Ultrasonic tracking will expand into wearables and smart home devices, creating a seamless (and invasive) behavioral profiling network. Expect regulatory pushback—but until then, users must take defensive action.
Defense Checklist:
✅ Disable TV tracking settings
✅ Block ultrasonic domains at the router
✅ Audit app permissions regularly
✅ Use signal-jamming apps (e.g., Ultrasonic Blocker)
Stay vigilant—your devices are listening, even if you can’t hear them.
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Sam Bent – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
