Secret Service Bought Phone Location Data from Apps, Contract Confirms:

“A myriad of smartphone apps, from weather predictors, to games, to flashlights, collect location data. Sometimes this may provide some benefit to the app’s operation itself, such as being able to route directions from a users’ current location, but many of these apps often sell that information as well to data brokers or other companies who incorporate it into their own products.”

an agency does not need to seek a warrant when it simply buys the data instead.