Last week, the state of cellphone tracking became slightly more confusing. The U.S. Department of Justice announced that, except in emergency situations, federal agents would now seek warrants before using "Stingrays." Stingrays are devices that mimic cellphone towers and can pinpoint a phone’s physical location or record which number they’re calling.

For people who follow the issue closely, like the ACLU, the news was welcome if limited. But for many, it made the situation around cellphone surveillance even trickier than it was before. How many different ways can the government surveil cellphones? What can each method do? Here’s a primer.

If law enforcement wants to surveil your cellphone, they have two ways to do it. They can do it through a phone company; or they can do it directly, using a device like a Stingray.

Let’s talk about the first way. If the government goes through the phone company, they probably do it by seeking cell-site location information, or CSLI. CSLI is created whenever a cellphone talks to a cell tower: It’s a record of towers that a cellphone pinged, what direction the cellphone’s ping came from, and what time the ping came.

Police seek three different kinds of CSLI. The first is historical CSLI, when detectives ask for days, weeks, or months of this kind of location data from the past. This is an extremely common process: From January to June 2015, Verizon received more than 21,000 requests of this type. Right now, this kind of process doesn’t require a warrant in most jurisdictions. (The courts don’t completely agree on the law around this technology, though, so the Supreme Court could wind up weighing in on the issue soon.) The second kind of CSLI is "prospective" or “real-time.” Law-enforcement agents might ask a mobile provider for a phone’s current location or its upcoming week of pings. They might also demand that the provider send a ping to the phone right now, generating its own record of CSLI. This type of search usually does require a warrant. The third type of CSLI is called a "tower dump," and it works more like a dragnet. Authorities will ask a provider for all the CSLI from a tower or towers from a certain period, then comb through that looking for a common number. (They’d be investigating a question like: Which cellphone numbers were near this bank an hour before or after it was robbed?) Hanni Fakhoury, a senior staff attorney at the Electronic Frontier Foundation, told me there was very little case law on this kind of search, but that, in the one relevant court ruling he knew of, a warrant was not required.