A US court is looking at whether the US government's use of a "Stingray" surveillance device was right.
The case, the United States v. Rigmaiden, is being closely watched and, according to the watchdog the Electronic Frontier Foundation, leaves the government with some explaining to do.
"Stingray" is the brand name of an International Mobile Subscriber Identity locator, or "IMSI catcher". It acts as a fake mobile phone tower which sits in a van outside a person's house, allowing the government to route all network traffic to the fake tower.
The EFF does not like Stingray because they can obtain the contents of electronic and wire communications while necessarily sucking down data on scores of innocent people along the way.
Daniel David Rigmaiden is charged with a variety of tax and wire fraud crimes, but the spooks could not pinpoint Rigmaiden's precise location within an apartment building.
The FBI obtained a court order to force Verizon to help the agents pinpoint the physical location of a wireless broadband access card and mobile phone they believed Rigmaiden was using.
However, the government did not just get Verizon to give it the data. It also used a Stingray device to find Rigmaiden, and got its paws on a lot of other data from other electronic devices in the complex as well, which it deleted.
Rigmaiden claimed that the Stingray evidence was a warrantless search in violation of the Fourth Amendment. But the EFF pointed out that the warrant only mentioned Verizon and did not allow for Stingray to be used.
The fact that it captured loads of information from other people not suspected of criminal activity it was a "general warrant," the precise evil the Fourth Amendment was designed to prevent, the EFF said.