The rapid rise of mobile health technologies, such as smartphone apps and wearable sensors, presents psychiatry with new tools of potential value in caring for patients. Novel diagnostic and therapeutic applications of these technologies have been developed in private industry and utilized in mental health, although these methods do not yet constitute standard of care. In this article, we provide an ethical perspective on the practical use of this novel modality by psychiatrists. We propose that in the present context of limited scientific research and regulatory oversight, mobile technologies should serve to enhance the psychiatrist-patient relationship, rather than replace it, to minimize potential clinical and ethical harm to vulnerable patients. We analyze areas of possible ethical tension between clinical practice and the consumer-driven mobile industry, and develop a decision-tree model for implementing ethical safeguards in practice, focused on managing risk to the therapeutic relationship, informed consent, confidentiality, and mutual alignment of treatment goals and expectations.