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.

翻译：无线传感技术现已能够利用射频与声学信号检测心跳，引发了显著的隐私担忧。现有隐私解决方案要么不加区分地防御所有传感系统，从而完全阻断任何实用功能，要么仅在数据收集后操作，无法实现选择性访问——即授权设备可监测，而未授权设备则不能。我们提出一种基于密钥的物理混淆系统PrivyWave，通过在密码学确定的频率上生成受控的伪装心跳信号来应对这一挑战。未授权传感器接收到的真实信号与伪装信号混合，若无密钥则无法区分；而授权传感器则利用密钥滤除伪装信号，恢复精确测量。我们对13名参与者的评估表明，该系统在两种传感模态下均能提供有效保护：对于毫米波雷达，未授权传感器的平均绝对误差为21.3次/分钟，而授权传感器则保持在更低的5.8次/分钟；对于声学传感，未授权误差增至42.0次/分钟，授权传感器则达到9.7次/分钟。该系统无需针对各模态定制即可跨多种传感模式运行，并提供密码学混淆保证。性能基准测试显示，在不同距离（30-150厘米）、方向（120°视场角）及多样室内环境中均具备稳健的保护能力，从而确立了物理层混淆作为普适健康监测中实现选择性隐私的可行途径。