Court: Locating suspect via stingray requires a warrant
arstechnica.com
arstechnica.com
So then they don't _necessarily_ require a warrant. It seems like nowadays, with the Patriot Act and similar law measures, you would have to completely ban in all cases something you don't want authorities to abuse. Otherwise, they will have an excuse for being unconstitutional they can take advantage of.
In the criminal procedure context, exigent circumstance means the following: An emergency situation requiring swift action to prevent imminent danger to life or serious damage to property, or to forestall the imminent escape of a suspect, or destruction of evidence.
Seems reasonable to me
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...
It seems like they would probably be arguing for this one.