  Consumer Internet of Things (IoT) devices are extremely popular, providing
users with rich and diverse functionalities, from voice assistants to home
appliances. These functionalities often come with significant privacy and
security risks, with notable recent large scale coordinated global attacks
disrupting large service providers. Thus, an important first step to address
these risks is to know what IoT devices are where in a network. While some
limited solutions exist, a key question is whether device discovery can be done
by Internet service providers that only see sampled flow statistics. In
particular, it is challenging for an ISP to efficiently and effectively track
and trace activity from IoT devices deployed by its millions of subscribers
--all with sampled network data.
  In this paper, we develop and evaluate a scalable methodology to accurately
detect and monitor IoT devices at subscriber lines with limited, highly sampled
data in-the-wild. Our findings indicate that millions of IoT devices are
detectable and identifiable within hours, both at a major ISP as well as an
IXP, using passive, sparsely sampled network flow headers. Our methodology is
able to detect devices from more than 77% of the studied IoT manufacturers,
including popular devices such as smart speakers. While our methodology is
effective for providing network analytics, it also highlights significant
privacy consequences.
