https://www.techdirt.com/articles/20211029/17155547844/document-freed-foia-shows-how-much-data-fbi-can-obtain-cellphone-service-providers.shtml

An internal FBI document shared with Joseph Cox of Motherboard by Ryan Shapiro of Property of the People gives a little more insight into law enforcement's data grabs. The Third Party Doctrine -- ushered into law by the Supreme Court decision that said anything voluntarily shared with third parties could be obtained without a warrant -- still governs a lot of these collections.

For everything else, there are warrant exceptions, plain view, inevitable discovery, a variety of "exigent circumstances," and reverse warrants that convert probable cause to "round up everyone and we'll decide who the 'usual suspects' are." Constitutional concerns still reside in this gray area, which means law enforcement will grab everything it can until precedent says it can't.