Smartphones are ubiquitous in modern society; in 2021, the number of active subscriptions surpassed 6 billion. These devices have become more than a means of communication; smartphones are powerful, continuously connected, miniaturized computers capable of passively and actively collecting (private) information for us and from us. Their implementation as detectors or instrumental interfaces in emerging smartphone-based (bio)sensors (SbSs) has facilitated a shift towards portable point-of-care platforms for healthcare and point-of-need systems for food safety, environmental monitoring, and forensic applications. These familiar, handheld devices have the capacity to popularize analytical chemistry by simplifying complicated laboratory protocols and automating advanced data handling without requiring expensive equipment or trained analysts. To elucidate the technological, legal, and ethical challenges associated with developing SbSs, we reviewed the existing literature (2016–2021), providing an in-depth critical analysis of state-of-the-art optical and electrochemical SbSs. This analysis revealed the key areas to consider for emerging SbSs, which we will address in a set of review papers. Part I (this review) will consider (i) how the SbS data are acquired and processed and (ii) the implementation of privacy and data protection strategies to keep this data secure. Part II will then focus on (iii) the development and validation of biosensors and (iv) how to assess the usability and (potential) social impact of emerging SbSs. Finally, these insights are applied to generate, for the first time, proposed best practices to help guide the future ethical data handling and development of smartphone-based devices for analytical chemistry applications.