The US government isn’t allowed to wiretap American citizens without a warrant from a judge. But there are plenty of legal ways for law enforcement, from the local sheriff to the FBI, to snoop on the digital trails you create every day. Authorities can often obtain your e-mails and texts by going to Google or AT&T with a simple subpoena. Usually you won’t even be notified. The Senate last week took a step toward updating privacy protection for emails, but it's likely the issue will be kicked to the next Congress. In the meantime, here’s how police can track you without a warrant now:

Stuff they can get

Phone records: Who you called, when you called

How they can get it: Listening to your phone calls without a judge's warrant is illegal if you're a US citizen. But police don't need a warrant—which requires showing "probable cause" of a crime—to get just the numbers you called and when you called them, as well as incoming calls, from phone carriers. Instead, police can get courts to sign off on a subpoena, which only requires that the data they're after is relevant to an investigation—a lesser standard of evidence.

What the law says: Police can get phone records without a warrant thanks to Smith v. Maryland, a Supreme Court ruling in 1979, which found that the Constitution's Fourth Amendment protection against unreasonable search and seizure doesn't apply to a list of phone numbers. The New York Times reported last week that the New York's police department "has quietly amassed a trove" of call records by routinely issuing subpoenas for them from phones that had been reported stolen. According to The Times, the records "could conceivably be used for any investigative purpose."

Location data: Your phone is a tracker

How they get it: Many cell phone carriers provide authorities with a phone's location and may charge a fee for doing so. Cell towers track where your phone is at any moment, and so can the GPS features in some smartphones. The major cell carriers, including Verizon and AT&T, responded to at least 1.3 million law enforcement requests for cell phone locations, text messages and other data in 2011. Internet service providers can also provide location data that tracks users via their computer's IP address—a unique number assigned to each computer.

What the law says: Many courts have ruled that police don't need a warrant from a judge to get cell phone location data. They only have to show that, under the federal Electronic Communications Privacy Act (EPCA), the data contains "specific and articulable facts" related to an investigation—again, a lesser standard than probable cause. Delaware, Maryland and Oklahoma have proposed laws that would require police to obtain a warrant for location data; Gov. Jerry Brown of California, a Democrat, vetoed a similar bill in September. Last week, the Senate Judiciary Committee approved a bill championed by Sen. Patrick Leahy (D-VT), to update the ECPA, but it would not change how location data is treated.

IP addresses: What computers you used

How they get it: Google, Yahoo, Microsoft and other webmail providers accumulate massive amounts of data about our digital wanderings. A warrant is needed for access to some e-mails (see below), but not for the IP addresses of the computers used to log into your mail account or surf the Web. According to the American Civil Liberties Union, those records are kept for at least a year.

What the law says: Police can thank US v. Forrester, a case involving two men trying to set up a drug lab in California, for the ease of access. In the 2007 case, the government successfully argued that tracking IP addresses was no different from installing a device to track every telephone number dialed by a given phone (which is legal). Police only need a court to sign off on a subpoena certifying that the data they're after is relevant to an investigation—the same standard as for cell phone records.

E-mails: Messages you sent months ago

How they get it: There's a double standard when it comes to e-mail, one of the most requested types of data. A warrant is needed to get recent e-mails, but law enforcement can obtain older ones with only a subpoena. Google says it received 7,969 requests for data—including e-mails sent through its Gmail service—from US law enforcement in the first half of 2012 alone. Other e-mail providers have not made similar statistics available.

What the law says: This is another area where the ECPA comes into play. The law gives greater protection to recent messages than older ones, using a 180-day cutoff. Only a subpoena is required for e-mails older than that; otherwise, a warrant is necessary. The Leahy bill would require a warrant to get all e-mails regardless of age.

E-mail drafts: Drafts are different

How they get it: Communicating through draft e-mails, à la David Petreaus and Paula Broadwell, seems sneaky. But drafts are actually easier for investigators to get than recently sent e-mails because the law treats them differently.

What the law says: The ECPA distinguishes between communications—e-mails, texts, etc.—and stored electronic data. Draft e-mails fall into the latter, which get less protection under the law. Authorities need only a subpoena for them. The Leahy bill would change that by requiring a warrant to obtain them.

Text messages: As with e-mails, so with texts

How they get it: Investigators need only a subpoena, not a warrant, to get text messages more than 180 days old from a cell provider—the same standard as e-mails. Many carriers charge authorities a fee to provide texts and other information. For texts, Sprint charges $30, for example, while Verizon charges $50.

What the law says: The ECPA also applies to text messages, according to Hanni Fakhoury, a lawyer with the Electronic Frontier Foundation, which is why the rules are similar to those governing e-mails. But the ECPA doesn't apply when it comes to actually reading texts on someone's phone rather than getting them from a carrier. State courts have split on the issue. Ohio's Supreme Court has ruled that police need a warrant to view the contents of cell phones of people who've been arrested, including texts. But the California Supreme Court has said no warrant is needed. The US Supreme Court in 2010 declined to clear up the matter.

Cloud data: Documents, photos, and other stuff stored online

How they get it: Authorities typically need only a subpoena to get data from Google Drive, Dropbox, SkyDrive, and other services that allow users to store data on their servers, or "in the cloud," as it's known.

What the law says: The law treats cloud data the same as draft e-mails—authorities don't need a warrant to get it. But files that you've shared with others—say, a collaboration using Google Docs—might require a warrant under the ECPA if it's considered "communication" rather than stored data. "That's a very hard rule to apply," says Greg Nojeim, a senior counsel with the Center for Democracy and Technology. "It actually makes no sense for the way we communicate today."

Social media: The new privacy frontier

How they get it: When it comes to sites like Facebook, Twitter and LinkedIn, the social networks' privacy policies dictate how cooperative they are in handing over users' data. Facebook says it requires a warrant from a judge to disclose a user's "messages, photos, videos, wall posts, and location information." But it will supply basic information, such as a user's e-mail address or the IP addresses of the computers from which someone recently accessed an account, under a subpoena. Twitter reported in July that it had received 679 requests for user information from US authorities during the first six months of 2012. Twitter says that "non-public information about Twitter users is not released except as lawfully required by appropriate legal process such as a subpoena, court order, or other valid legal process."

What the law says: Courts haven't issued a definitive ruling on social media. In September, a Manhattan Criminal Court judge upheld a prosecutor's subpoena for information from Twitter about an Occupy Wall Street protester arrested on the Brooklyn Bridge in 2011. It was the first time a judge had allowed prosecutors to use a subpoena to get information from Twitter rather than forcing them to get a warrant; the case is ongoing.