Digitalization affects the relation between human agents and technological objects. This paper looks at digital behavior change technologies (BCT) from a deontological perspective. It identifies three moral requirements that are relevant for ethical approaches in the tradition of Kantian deontology: epistemic rationalism, motivational rationalism and deliberational rationalism. It argues that traditional Kantian ethics assumes human ‘subjects’ to be autonomous agents, whereas ‘objects’ are mere passive tools. Digitalization, however, challenges this Cartesian subject-object dualism: digital technologies become more and more autonomous and take on agency. Similarly, human subjects can outsource agency and will-power to technologies. In addition, our intersubjective relations are being more and more shaped by digital technologies. The paper therefore re-examines the three categories ‘subject’, ‘object’ and ‘intersubjectivity’ in light of digital BCTs and suggests deontological guidelines for digital objects, digital subjects and a digitally mediated intersubjectivity, based on a re-examination of the requirements of epistemic, motivational and deliberational rationalism.