World-wide connectivity of all kinds of embedded devices and computers - the Internet of Things (IoT) - is opening new opportunities for everyday applications. However, connecting networked devices with limited user-interaction capabilities and interfaces securely to remote Internet services is challenging. Existing solutions for security pairing, based e.g. on passwords, trusted certification authorities, or physical connection, are not feasible when devices have long distance and have not interfaces for inputting passwords or secrets keys. This paper analyzes approaches for pairing these interface restricted devices. We explore challenges in device pairing in IoT and possibilities to use smartphones as mediators to establish security associations easily. We contribute by analyzing how user-friendly security establishment approaches - out-of-band or unauthenticated location-based pairing - can be applied in situations where a counterparty is far away or has incompatible interfaces.