This paper presents the Smart Device specification to interface with remote labs. To encourage the broader sharing of remote labs, the Smart Device paradigm decouples the client from the server and provides well-defined interfaces between client and server. Such Smart Device services are exposed on the Internet and enable interoperability with client applications, other Smart Devices and external services (e.g. a booking service). This papers presents the extensible and platform-agnostic specification of the Smart Device services and internal functionalities. The Smart Device specification contains sufficient service metadata to enable the automatic generation of basic client applications. The specification is illustrated through an example and first implementations of the specification are presented.