Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for presenting content items. In one aspect, a method includes identifying an opportunity to present a content item at a device and in a manner that precludes a user from accessing content of one or more applications executing on the device. Data relating to a status of each of the one or more applications are identified. A level of urgency for a user to access content of the one or more applications is determined based on the data. A response to the opportunity to present a content item is selected based on the level of urgency for the user to access content of the one or more applications. The response is selected from a first response that causes presentation of the content item and a second response that precludes presentation of the content item.