A class-action lawsuit filed Monday alleges that BART has been collecting personal information from people using BART Watch, a mobile app meant to help riders report crimes and get updates about the transit system. The complaint, filed in U.S. District Court in Oakland, alleges the “clandestine collection” of user data, including the “near constant” ability to locate a specific cellular device, by BART and the app’s Boston-based developer Elerts Corp. The lawsuit also says that BART and Elerts went against state privacy laws that require explicit warnings to users that their data may be collected.