The paper presents the specification, development and initial performance evaluation of the Simplicity Device (SD), which is one of the key components of the SIMPLICITY Architecture. The SD is both a portable personalization device and a hardware Single-Sign-On (SSO) token. It accommodates the Simplicity User Profile (SUP), which contains user context related information and has been designed according to 3GPP and W3C standards. In cooperation with a distributed brokerage framework the SD provides the users with the means to automatically personalize terminals and services according to their context by the simple act of “plugging” the SD into any SIMPLICITY compliant user equipment. Within this paper we present the generic SD architecture which is the basis for different SD implementations and consequently we focus on a JavaCard SD implementation and its performance evaluation.