Along with the proliferation of IoT devices, people have a lot of concerns on the privacy issues brought by them. Existing solutions, employing encryption or trying to hide the communication in PHY layer, often suffer from the limited capability of IoT devices. To address this issue, we propose Rustle, an acoustic communication design which builds covert connection among IoT devices using random noise. Noise signal can be easily generated and exchanged by the widely used speakers and microphones on IoT devices. Based on a fine-grained control of signal’s wave shape, Rustle generates a series of mutually uncorrelated random signals that contain “hidden patterns” to embed information. Extensive evaluations demonstrate that Rustle can achieve a lower than 1% BER while the eavesdropper’s error rate on detecting the signal is higher than 80%.