Mobile phone–based sensing software is a class of software for mobile phones that uses the phone's sensors to acquire data about the user. Some applications of this software include mental health and overall wellness monitoring. This class of software is important because it has the potential of providing a practical and low-cost approach to deliver psychological interventions for the prevention of mental health disorders,[1] as well as bringing such interventions to populations that have no access to traditional health care.[2] A number of terms are used for this approach, including "personal sensing", "digital phenotyping", and "context sensing". The term "personal sensing" is used in this article, as it conveys in simple language the aim of sensing personal behaviors, states, and conditions.