Unbeknownst to most cell phone users, just turning your cell phone on reveals your location. That’s because once turned on, your cell phone constantly “pings” (bounces a signal off of) nearby cell phone network towers. This data is collected by the cell phone company and can be traced to reveal your location.

Short of turning your cell phone off and maybe even pulling out its battery, there’s nothing you can do about this: This is just basic cell phone technology at work. Technology that can determine your physical whereabouts for as long as your cell phone is turned on, which for most of us means 24 hours a day.

So you were late to work this morning because you were at a job interview with your company’s competitor? This data can prove that. You went to visit your doctor about that nasty infection you’ve been fighting? It can confirm that. You stopped by your girlfriend’s house before picking your wife up for dinner? That too. 

Investigators know that your cell phone location records are a treasure trove of personal information.  That’s why many of them promise clients that they can ping cell phones, or offer to install spyware on a phone that can track its location, or remotely access a cell phone via Bluetooth technology. Having this information may undoubtedly help confirm that a spouse is being unfaithful, or that a once loyal employee is violating confidentiality agreements and sharing proprietary information with a competitor.

But that doesn’t mean it’s legal.

Investigators offering location based services often fail to mention that cell phone tracking by anyone other than the cell phone owner and law enforcement is illegal. As a general rule, unless the cell phone is registered in your name, pinging it yourself, asking the cell phone company to do it, or hiring a third-party service to do it on your behalf may violate privacy laws. 

Even within law enforcement, cell phone tracking is under the microscope: To date, the U.S. Courts of Appeals for the Third, Fifth and Sixth Circuits have considered whether warrantless cell phone location tracking by the government violates the Fourth Amendment, with varied results.  The Third Circuit ruled in 2010 that judges can demand a showing of probable cause when the government seeks cell phone tracking location data. The Sixth Circuit decided this summer that warrantless cell phone tracking by law enforcement does not constitute a search, therefore no warrant is necessary.  The oral arguments for the Fifth Circuit decision were held in October. Meanwhile, Congress is also weighing in on the matter.

If the cops aren’t allowed to track cell phone locations without a warrant, odds are the investigator who promises he can is crossing a line.

Some investigators also offer to obtain this data by using pretexting to trick a phone user into sharing their address or location. This is also a no-no. For instance, some investigators will contact cell phone users via text message or voice call, telling them that they are the winner of a contest, and asking that they text or call back or share their address or location in order to claim their prize.  This information is then used to determine the cell phone’s location data. But remember, attorneys and their agents are bound by several ethics rules that frown upon pretexting, so this little trick could also cause a pretty big mess.