Police used Moocherhunter to find other devices connected to the subscriber’s wireless router, which led them to Richard Stanley, who lived across the street from the subscriber. Police then used the Moocherhunter information to obtain a warrant to search Mr. Stanley’s home, and based on evidence they found, Mr. Stanley was indicted in November 2011 for possessing child pornography.

Mr. Stanley sought to suppress the evidence, arguing that police needed a warrant to use Moocherhunter to locate him. U.S. District Judge Joy Flowers Conti found that Mr. Stanley “could have no reasonable expectation of privacy in the signal he was sending to or receiving” from the wireless router.

“An internet subscriber does not have a reasonable expectation of privacy in his IP address or the information he provides to his Internet Service Provider, such as Comcast, in order to legally establish an internet connection, and likewise, a person connecting to another person’s wireless router does not have an expectation of privacy in that connection,” she wrote in a Nov. 14 order.

I'm not sure whether you should have a reasonable expectation of privacy in the location from which you are making a wireless transmission (a reasonable expectation against triangulation). I'm also positive that if you did, the police would have successfully obtained a warrant in this case. However, I'm also pretty sure that the argument quoted above is incorrect in its reasoning, if not in its conclusions (again, I'm not sure what the right conclusion is, but this reasoning doesn't get me there.)

The reason you don't have a reasonable expectation of privacy regarding your IP address and subscriber information is the third party rule - things that you've told your ISP, you've told the government, more or less. You haven't told a wireless access point what your physical location is, so if you have no reasonable expectation of privacy regarding that information, its for a totally different reason.

Update: OK, I think I figured out how this should work. The rule should be the same as for automobile searches - probable cause should be required but a warrant should not be required.

Wireless transmissions are fickle and transient. Police may need to act in the moment to triangulate them, and so the bureaucratic requirement for a warrant is too onerous and would not work in practice. However, people DO have a reasonable expectation of privacy regarding the physical source of their wireless transmissions, and the police should establish probable cause before triangulating them. Otherwise you have a situation where the police can monitor everyone's physical movements all the time by tracking their cellphones, and that ain't gonna work. There are several case precedents that could be used to buttress both positions.

In this case the police had probable cause. They didn't get a warrant, but they didn't need to. The triangulation of the defendant's wireless signal was proper and the evidence should not be suppressed.

Can Police Locate Wireless Internet Moochers Without a Warrant? - Law Blog - WSJ