Smartphone users are offered a plethora of applications providing services, such as games and entertainment. In 2018, 94% of applications on Google Play were advertised as “free”. However, many of these applications obtain undefined amounts of personal information from unaware users. In this paper, we introduce transiency: a privacy-enhancing feature that prevents applications from running unless explicitly opened by the user. Transient applications can only collect sensitive user information while they are being used, and remain disabled otherwise. We show that a transient app would not be able to detect a sensitive user activity, such as a daily commute to work, unless it was used during the activity. We define characteristics of transient applications and find that, of the top 100 free apps on Google Play, 88 could be made transient. By allowing the user to decide when to allow an app to collect their data, we move towards a fair trade of personal information for application services.