Linda Lye of the ACLU writes:
The ACLU and Electronic Frontier Foundation have filed an amicus brief in what will be the first case in the country to address the constitutional implications of a so-called “stingray,” a little known device that can be used to track a suspect’s location and engage in other types of surveillance. We argue that if the government wants to use invasive surveillance technology like this, it must explain the technology to the courts so they can perform their judicial oversight function as required by the Constitution.
The case is highly significant for two reasons. First, it shows that the government is using new types of technology—not just GPS and cell site location records—to track location. Second, it shows that the government is going to great lengths to keep its surveillance practices secret.
Read more on ACLU.