PrivyWave: Privacy-Aware Wireless Sensing of Heartbeat

TL;DR

PrivyWave is a physical-layer privacy system for wireless heartbeat sensing that uses cryptographic decoy signals to enable selective access for authorized devices while protecting against unauthorized sensors.

Contribution

It introduces a novel key-based physical obfuscation method that generates decoy signals, allowing selective privacy in wireless heartbeat sensing across multiple modalities.

Findings

Unauthorized sensors have significantly higher error rates (21.3-42.0 BPM)

Authorized sensors maintain accurate measurements (5.8-9.7 BPM)

Effective privacy protection across various environments and distances

Abstract

Wireless sensing technologies can now detect heartbeats using radio frequency and acoustic signals, raising significant privacy concerns. Existing privacy solutions either protect from all sensing systems indiscriminately preventing any utility or operate post-data collection, failing to enable selective access where authorized devices can monitor while unauthorized ones cannot. We present a key-based physical obfuscation system, PrivyWave, that addresses this challenge by generating controlled decoy heartbeat signals at cryptographically-determined frequencies. Unauthorized sensors receive a mixture of real and decoy signals that are indistinguishable without the secret key, while authorized sensors use the key to filter out decoys and recover accurate measurements. Our evaluation with 13 participants demonstrates effective protection across both sensing modalities: for mmWave radar, unauthorized sensors show 21.3 BPM mean absolute error while authorized sensors maintain a much smaller 5.8 BPM; for acoustic sensing, unauthorized error increases to 42.0 BPM while authorized sensors achieve 9.7 BPM. The system operates across multiple sensing modalities without per-modality customization and provides cryptographic obfuscation guarantees. Performance benchmarks show robust protection across different distances (30-150 cm), orientations (120{\deg} field of view), and diverse indoor environments, establishing physical-layer obfuscation as a viable approach for selective privacy in pervasive health monitoring.