Everyone is all aflutter about the news that Steve Jobs knows where you have been. Since that Earth-shattering bit of news, a lot of bloggers and reporters have pointed out how other software within the iPhone can do the same thing without the user realizing it, and how the Android devices do this as well. Greg Laden has a good summary of these articles in his post iKnowwhatyoudidlastsummer.

To be blunt, people being tracked in their everyday lives is nothing particularly new. I'm happy that this has made a splash in the mass media since it's a situation that has been increasing in prevalence without major notice until now. When I teach IT security, I always spend some time covering privacy issues as well, and have discussed tracking issues regularly for fifteen years now.

A common thought problem I would often give to my students is to plan a cross country road trip in such a way that they could not be tracked. Fifteen years ago this was an interesting problem that forced people to think about how they interacted with a variety of databases. Today, it's a more difficult proposition to even accomplish.

Even before the advent of modern smart phones, people have been automatically tracked. When you use your debit or credit card, the bank has a primitive tracking record of your movements. The more you use it, the better the tracking. So, before leaving on a hypothetical un-tracked trip, you need to remember to leave these cards at home. You will need to work with cash. If you don't want to tip your bank off to your trip, you need to collect the cash in advance, a little at a time. It may also be a good idea to give your cards to a trusted friend so there is local activity on them while you are away, electronically geo-tagging you to your home town.

You can't just leave your smart phone at home; you will need to leave any cell phone behind. Cell phones have been tracked since the very first cell phone. Cell phones work by having the towers (and thus cell companies) track the phones. When you first turn on your phone, it sends a message out. Any nearby towers receive that signal, which then talk to a computer at the company. The tower with the strongest signal (as well as reasonably bandwidth, consistent signal, and other factors) will be granted sole authority over your phone. This process is periodically repeated in case you move. The cell company must always know which tower to direct a call through to get to your phone.

Ten years ago the cell companies swore to us on a stack of their own quarterly reports that this tracking data was not stored in any reasonably permanent way due to the amount of data and cost of storage. I haven't heard much about this as the cost of storage has plummeted, but I was always leery of the argument since it was based upon no compression of data that is easily compressed anyway. After 9/11 there was a lot of discussion about phone companies not destroying data that had been previously been destroyed. The problem now, of course, is finding out what data is actually stored today since that information is considered national security.

The difference with a modern smart phone is the introduction of a GPS chip that can provide better accuracy of your location. Still, accuracy of tower-only location services has gotten so good that several years ago governments began requiring cell phone companies to upgrade all of their towers so they can triangulate your position (using signals from multiple towers) to better coordinate emergency response when you call 911. While this works great when you get into an accident and want the government to find you, but it also means you can be tracked at all times to a surprising level of accuracy.

So, you will need to stop your phone from even communicating with a cell tower even if it's not a smart GPS-enabled phone. You can turn it off, but I never trust computers that have to monitor for a key press to be truly "off". You can remove the battery (assuming that's an easy thing to do). You could tightly wrap the phone in aluminum foil, then drop it in a Mylar bag. Or, I suppose, you could drop it in a river and walk away, which is probably the most satisfying way to stop a cell phone from tracking you.

Now, ready for your trip? Not quite yet.

Does your car have a tracking device and cell phone secretly stashed away behind a door panel? If it does, it may not mean you have an enemy agent in a black helicopter tracking your every move, it may just mean you have OnStar, or a similar system, installed by the auto manufacturer. That system is, basically, a tracking device attached to a cell phone integrated with your car's computer system. You should be able to locate the fuse which powers that module and remove it, or, if you are really paranoid, dismantle the panel it's mounted under and chuck it into the same river as your cell phone.

Now it's time to plan your route, and this is where things get complex.

If you live in a major city, especially Chicago or London, it can be difficult to find a route out of town where your license plate will not be recorded as you pass through an intersection. Many early red-light cameras would only take pictures when triggered by sensors, yet simple observation shows that such sensors are often triggered even when no one is running a light, such as when people turn right on red, or go over a sensor when turning left. In addition to that, many intersections now have cameras that simply record all traffic flow at all times. You need to avoid all such intersections.

The camera problem is made worse by projects such as the Chicago OEMC initiative which links private cameras into the Chicago Office of Emergency Management and Communications system for recording and monitoring. Even if you trust that your local 7-11 will destroy its security recordings, those same recordings may be saved by the government automatically.

On your trip toll roads, obviously, are a very bad idea. Even if you threw your toll authority Radio Frequency ID transceiver into the same river after your cell phone, cameras record every license plate passing through every toll plaza. By the way, if you ever want to prove your spouse was cheating on you, or they are a bad parent by working too late, you can subpoena their toll records for evidence.

Off the toll ways (and major expressways which may have traffic cameras, though the older systems don't have the resolution for picking up license plates), you need to be careful about any city, town or county you pass through with cameras. They are now so prevalent, you most likely need to do scouting trips to find a clear route.

Once you have arrived, you may be able to walk around anonymously for now. If it's in a big city, you can leave your car somewhere (Where? That's another problem) and use taxis. At the moment you don't really have to worry about automatic facial identification too much. While the technology is certainly impressive, unless someone has a good picture of your face and is specifically looking for you, such system won't be a help. They can find matches for specific people, but, as of yet, can't just identify all people passing in front of them.

One last piece of advice is to make sure you don't use your supermarket loyalty card when buying an apple in your destination city. Of course loyalty cards are a whole new privacy problem in themselves.

Ready for the return trip or do you just want to follow your cell phone into the river?

A California Court of Appeals judge recently ruled in People v. Lieng that there's no constitutional problem with police using night vision goggles to see things that they couldn't otherwise see. In Kyllo v. United States the Supreme Court had ruled that police could not use a thermal imaging device without a warrant, and you'd think the same rule would apply here, but it doesn't. The court's two-part explanation for this is entertainingly bizarre.

Consider the first part:

Kyllo is inapplicable to this case.  First, night goggles are commonly used by the military, police and border patrol, and they are available to the general public via Internet sales...More economical night vision goggles are available at sporting goods stores...Therefore, unlike thermal imaging devices, night vision goggles are available for general public use.

[citations elided]

Scott Greenfield explains part of the problem with this reasoning in a post titled "The Amazon Exception."  (In this excerpt, Scott calls night-vision goggles "nogs" because someone told him that's what all the cool kids are calling them.)

That nogs are used by the military, police and border patrol, fails to impress.  Lots of technology is used by government agents. Much of it is used to do nasty stuff that would, in the absence of a warrant, violate the Constitution.  So what?

But the kicker is that it's "available to the general public via internet sales."  Now it's getting interesting. When courts rely on the inventory at Amazon, or perhaps more obscure websites, for the scope of the 4th Amendment, there might be a problem.

No kidding there might be a problem. In this country, we supposedly have something called rule-of-law, which means we are not subject to the arbitrary whims and favors of despots and bureaucrats, but rather all people are held to a set of laws that are known in advance. But if the constitutionality of a search depends on something as vague as whether the tools used are "available to the general public," then who can know what the law means? Almost everything is available to the general public if they're willing to make some amount of effort, so who could possibly predict when a court might take notice?

Or as Scott says,

Rather than research the caselaw to determine whether police use of technology constitutes an unlawful search under the Fourth Amendment, we should begin our inquiry on Amazon. Is that the point?

Then there's the second part of the court's justification. Because I'm a science geek, I find it even more troublesome than the first part:

Second, state and federal courts addressing the use of night vision goggles since Kyllo have discussed the significant technological differences between the thermal imaging device used in Kyllo, and night vision goggles...Night vision goggles do not penetrate walls, detect something that would otherwise be invisible, or provide information that would otherwise require physical intrusion...The goggles merely amplify ambient light to see something that is already exposed to public view...This type of technology is no more "intrusive" than binoculars or flashlights, and courts have routinely approved the use of flashlights and binoculars by law enforcement officials.

The way this is written, the statement that "night vision goggles do not penetrate walls...or provide information that would otherwise require physical intrusion" seems to imply that thermal imaging does both of those things. As a matter of physics, that's just not true. Thermal imaging cannot see through walls.

What thermal imaging can do is tell you the temperature of those walls, which may give you some idea of what's on the other side. Put a heat source in a room, and the room will warm up. That will warm the inner surface of the room's walls, and some of that heat will leak through the walls to heat the outer surface of the building. Then, like everything else in the universe that has a temperature, the outer surface of the building will give off electromagnetic radiation.

The spectrum of that radiation--the portion of energy given off at various frequencies--depends mostly on the temperature of the radiating object. Sufficiently hot objects--usually around 900 degrees F°--give off electromagnetic radiation at frequencies high enough for humans to see--visible light--and the object appears to be glowing a faint red. Objects that are even hotter will give off other colors of the spectrum until you see an even mix of colors, meaning the object glows white hot.

Cooler objects give off light (electromagnetic radiation) that has frequencies too low to be detected by the human eye. We call this light infrared, meaning "below red." Infrared light behaves a lot like ordinary light, except that you just can't see it. And, just like ordinary light, it can't go through walls.

Getting back to the subject of this post, thermal imaging systems work by using electronic sensors to detect the low-frequency infrared light emitted from warm objects. The data from the sensor is used to create an image that is displayed to the user. Night vision systems, on the other hand, detect light that is in the visible part of the spectrum, but they use a sensor mechanism that can create an image from far less light than the human eye needs. Thus the main difference between the two technologies is that night vision works on light that is too dim for humans to see, whereas thermal imaging works on light that is the wrong frequency for humans to see.

That doesn't seem like a distinction important enough for a constitutional right to hinge on, but it makes more sense than what the judge wrote.

On the other hand, perhaps because I think of this too much in terms of the physics, I've never had a clear understanding of the principles by which the courts have ruled that thermal imaging requires a warrant. Why should police need a warrant to examine energy emissions that a suspect is allowing to just radiate away? If the subject is standing in his house and yelling about his drug grow operation at the top of his lungs, should the police get warrant before they're allowed to stand outside the house and listen? If not, then why should they need a warrant to detect infrared emissions outside the house?

If you don't want people to know about your drug-growing business, you should control your infrared emissions. Don't let your house radiate infrared energy through the air, where it could strike a sensor being held by a cop who's sitting in his car on the street. You're essentially sending signals to anyone with a receiver, so how is that an intrusion on your privacy?

Note that we can still rule out surveilance technologies that are intrusive--x-rays, penetrating radar, megnetic resonance--on the grounds that they involve sending something inside private property. They're the logical equivalent of a cop standing outside your house and using a long stick to reach in a window and poke around in your belongings, which I assume would require a warrant just as if he had entered.

The basic distinction is that the police can use passive technology to monitor emissions passively, but they can't actively send anything into an area they're not allowed to enter themselves.

This particular way of thinking about surveilance methods draws a fairly bright line for law enforcement and the courts to follow, but I can think of at least three consequences which are probably worth thinking about.

First of all, as a libertarian, I'm very worried about how much surveilance this does allow. Not only does it allow an unlimited amount of passive surveilance in the visible and infrared bands, it also seems to allow a lot of sophisticated listening devices. (Sound is vibrations in air rather than electromagnetic radiation, but the same principles seem to make sense.) For example, sounds inside a building, including conversation, will leak out as very subtle vibrations which are normally lost in the noise. It's theoretically possible, however, that an array of sensitive microphones and some very sophisticated signal processing technology could recover the original conversation.

Second, this rule would also allow police to listen to radio transmissions, including cell phones, without a warrant. I think I'm actually okay with this. Before the widespread use of cell phones, it was widely understood that everyone was legally permitted to receive any radio transmission they wanted to. After all, if other people transmitted radio signals in all directions, and some of those signals entered your house, it was pretty ridiculous to claim that tuning a receiver to pick them up was a violation of privacy. It was a simple concept that I'd like to see us return to: If you want privacy, don't transmit your conversation to everyone within range.

Third, the rule against actively sending something into a private area would seem to rule out a police officer shining a flashlight into window of a building or even a car. That seems a bit ridiculous, even to me. In addition, it would lead to all kinds of ridiculous situations as the police try to work around it. E.g. what if the police officer wears a white windbraker jacket and his partner shines the patrol car's spotlight on him--ostensibly to make sure he's safe--causing reflected light from the jacket to shine in a window? Alternatively, if flashlights are allowed, then what about using an infrared flashlight to illuminate a scene for viewing with a thermal imager? This could turn nutty very quickly.

At this point, I kind of have to give up. I can't seem to come up with a distinction that makes sense in terms of the physics involved and yet still offers adequate protection of privacy. Maybe the laws of physics are the wrong tools for figuring out things like this, or maybe vague and inconsistent rules made from case to case are the best we can do. I'd like to think that the law should make sense in terms of physics, but I'm not sure I have a good reason for believing that.