The Internet of Things (IoT) is hot right now. One of the common requirements that seems to be universal with regards to IoT is the need for security. Although it includes functional aspects, security — or rather, lack of security — is an emerging system property that cannot simply be realized by integrating a single, magic security IP block into your system. This paper provides an overview of security basics, feature requirements, technical solutions, and associated system-level trade-offs for implementing security in IoT devices. Making the required trade-offs is significantly easier by leveraging secure, proven building blocks that were designed with secure systems in mind and optimized for low footprint and energy. With the insights of this paper, trade-offs for a specific IoT device can be made more easily, the optimal mix of features can be decided on, and the resulting secure architecture can be implemented efficiently.