Developing a smartphone 'app' for public health research: the example of measuring observed smoking in vehicles.

Background: We have developed manual methods to gather data on the point prevalence of observed smoking in road vehicles. To enable the widespread international collection of such data, we aimed to develop a smartphone application (app) for this work.

Methods: We developed specifications for an app that described the: (1) variables that could be collected; (2) transfer of data to an online repository; (3) user interface (including visual schematics) and (4) processes to ensure the data authenticity from distant observers.