[mikeash]

There's a little more to the story than that. The suspect was in an apartment building surrounded by police, armed and dangerous. He lived in the building but wasn't in his apartment. The police were in the process of searching other apartments when they used the Stingray to locate him.

The argument made by the suspect is that the police should have obtained a warrant first because they had enough time to. There seems to be some merit to this (they had enough time to obtain search warrants for specific apartments) but that's something of a different question.

The story is discussed in detail in the order starting around page 20 here: https://www.documentcloud.org/documents/3962321-Gov-Uscourts...