How much do you trust your cellphone carrier or its manufacturer? They know a lot about you, and policymakers will learn today (May 10) at a Senate hearing how much information these companies are collecting related to our everyday travels.

Osama Bin Laden and his couriers discovered the hard way how effective cellphones can be at pinpointing locations. Bob Woodward’s piece in Friday’s Washington Post said the man who led US forces to Bin Laden’s location was so frightened of being tracked that he didn’t put the battery into his phone until he was an hour and a half away from the terrorist’s hideout. Even at that distance, it was enough for the intelligence community to put the pieces together.

But while most consumers have no reason to fear a Predator drone tracking their cellphone calls, it was revealed this month that both Google and Apple have been quietly collecting “anonymized” location data from tens of millions of their smartphones worldwide. Apple’s devices even went so far as to keep an unencrypted database—including a day-by-day summary—of the device’s prior locations. Apple quickly patched the location database issue in a recent iOS update, but its phones are still transmitting their locations back to the “mothership” on a regular basis.

The companies claim the data they collect is anonymous, and that nothing identifiable from the phone is sent back to company servers. Nevertheless, a Wall Street Journal report says that in the case of Google’s Android phones, a unique identifier also is sent along with the location data.

However, the WSJ report is “erroneous,” according to Google spokesman Chris Gaither, who adds that the Android location data sent to the company “is not tied or traceable to a specific user.”

Gaither added that the location data transmission operates on an “opt-in” basis, and that the company discloses it is collecting this data upon the device’s activation. However, the option to transmit the phone’s location data to Google is checked on by default when users opt to use location-based services. Gaither was unwilling to go into additional detail before the company testifies before the Senate’s Judiciary Subcommittee on Privacy, Technology and the Law on May 10.

Apple, in its usual fashion, did not respond to multiple requests for comment. In a statement the company issued April 27, Apple said the only way to opt-out of their location data collection process was to turn off location services entirely. Apple also requested and received an extension of time to respond to Connecticut Attorney General George Jepsen’s request for information on their data collection practices.

Why do they need this data?

Local search is one of the untapped goldmines in cyberspace, with no clear market leader. Getting relevant information to users quickly is the name of the game, and all smartphones employ what’s known as “assisted GPS” to rapidly determine a user’s location.

Assisted GPS works by determining the location of cellphone towers but also increasingly WiFi hot spots. WiFi hot spots (including home routers) each have a unique serial number that is transmitted in the clear. If a phone conducts a location search and also is in range of a hotspot, that data is transmitted back to Apple and Google to help make future searches faster. Relying completely on GPS satellites can take minutes—assisted GPS can cut that time down to seconds or even milliseconds.

Opting out of the 21st Century?

It’s easy to forget that the cellphone carriers have been able to track customer locations for decades. After all, cellphones are essentially two-way radios that communicate with nearby towers. Carriers regularly turn over location data to authorities in response to warrants, subpoenas, and missing persons cases.

What’s changed is that this data has become increasingly more accurate, and consumer dependence on smartphones means they are almost always turned on – acting as a virtual homing beacon for billions of subscribers worldwide.

Ultimately owning no phone at all is the only way to truly remain “off-the-grid” in the 21st century. Even the world’s most wanted man couldn’t do that for long.