I used to know someone who claimed to work in the intelligence field, and although I've met several people over the years who claimed similar things, I believed this person. The reason I believed her is that I never was able to trip her up. She always referred to her employer as a well known intelligence service. I'd ask if she meant the CIA or the NSA and she'd never actually agree to anything verbally although in the course of the conversation it was easy enough to tell what she meant. There was a sound reason for her discreet behavior -- someone is listening. Always. That monitoring agency isn't a person or a team of persons. It's a voice recognition program that detects keywords in voice communications.

Because of the way our communications systems are built, there are junction points and other bottlenecks through which all data passes. At those points it's technically possible to listen to every conversation that passes through. That's physically impossible, if you rely on people. It would literally take one person per conversation, and with the amount of traffic in the system, that's out of the reach of any government's budget. We'd all have jobs listening to each other if that were being done.

On the other hand, a high speed computer with unlimited sets of electronic ears and lots of electronic memory has plenty of time for that. It just lacks the intelligence to understand what might be important in the things it hears. To identify individual voices or key words and phrases requires sophisticated surveillance software. Even then the computer will amass a huge amount of information it considers suspicious when it actually is not. Just because I write the acronym CIA, or say it over a phone line, there's no reason to think that anyone from that well known intelligence service will ever read this article. Lots of people use the term CIA in conversation. Think of the computer system which monitors the information flow as a drug sniffing dog. That term is enough to make it perk its ears up a bit, but not enough to make it bark.

But the computer is smart enough to add in other factors, and in the example I began with, the other major factor would be that my online friend worked for a major intelligence service which already knew a lot of things about her, including her home phone number and IP address. If she used key words the computer listened for, it was enough to make the big dog point. The big dog listened especially carefully to the things she said, because her IP address matched one on a list it consulted. If the people she spoke to talked about unacceptable things or she brought them up herself, the big dog would bark and a person would come running to see what was actually going on. The person would decide whether it was important or not.

In real life, the big dog isn't very smart. It barks at all sorts of things and can't really tell if people are kidding or blowing off steam or really are plotting the overthrow of the government. It detects certain sounds and patterns but does not understand what they mean. But it's really good at listening, and is it listening to you? Oh, yeah. Should you worry about that? A moderate amount of concern is warranted. Don't get paranoid about it, but don't be naive and think that this will all go away. The technology is here to stay and it gets better all the time. Be careful what you say, or you'll get put on a watch list. In reality there are probably so many other relatively innocent people on the same list that it will have no effect on your life at all, unless eventually you do something to justify being put there, or belong to an organization or ethnic group that fits a suspicious profile. Then your name will rise towards the top. It's not smart to be at the top of the list where people really pay attention to you.

The thing that most people are concerned about is much closer to home than the Big Dog software. For now we can safely ignore the Big Dog unless we really are doing something wrong. On a smaller scale in the world of wrong doing, most of us have private skeletons in our closets and don't want them to become public. From private intimate conversations to civil legal and business information, we have plenty of reasons to treasure our privacy. Technology threatens that, even when laws protect us.

It's true, the law is often still on your side when it comes to privacy of communications. If police have good reason to suspect your involvement in criminal activity, official permission can be granted for wiretaps of several kinds, many of which have nothing technically to do with wires or tapping. (Those terms literally apply to old technology which today is seldom used by anyone but amateurs). The laws regarding phone taps are very strict and ordinary citizens involved in legal activities should not be concerned they'll be targeted. On the other hand, if you have business secrets to protect or you are involved in an angry divorce proceeding, you may have reason for concern even if the law does say that you are protected. Some people don't care about that and at any rate would not intend to use direct results of the wiretap in court or in business. What they would want is information that leads to something else they can legally use.

So it is still possible that someone with those reasons in mind could physically tap into your phone system. The common urban lore is that a phone tap of this kind is something you can hear -- an unexplained background tone or warble that wasn't there before, or clicking and static that comes and goes. This is mostly urban legend, because the best of today's equipment isn't detectable. It's good enough that you'll never know it's there.

In ancient times, going back to the fifties and sixties when the Sean Connery James Bond was young, those things might actually have signaled a security breach. A recording device wired into the system might produce some audible feedback from its own circuitry, and a poorly connected surveillance tap might occasionally pop and crackle if the technician hadn't done a good job. Systems that directly connected to a phone line caused a noticeable drop in voltage on the line, because each listening device diverted part of the signal away from yours. When I was a kid and our only telephone was a party line, you'd hear a click when the neighbors picked up during your call and the volume would drop just a bit. If it was a really good call, enough people might be listening that you could barely hear the conversation. That's simplistic, but it's the same concept.

Detectors are still available that will measure an unexplained voltage drop, but they aren't worth the money. A thorough inspection of phone lines will reveal anything that crude. If you experience an unexplained drop in audio quality, get the phone company to check it out. If your line runs through a crawlspace you might have to check it out yourself. If you find a tape recorder next to the line that's a clue.

Most audio problems will turn out to be not at all related to home security. We suffered from all these issues for years and had many arguments with the phone company about them, although we never suspected or even mentioned the possibility of a phone tap. Technicians always found nothing in the areas they were employed to inspect and blamed the interference on computer noise from our PC. Though we knew that wasn't the problem, it's hard to argue with the phone company.

They were partly right. The phone problem wasn't in their territory. On a neighboring property a tree had died and a dead limb was brushing a power line, creating pops and crackles and static especially in wet and windy weather. Eventually it fell over and took down the power line, resolving most of our phone problems.

For more real concerns, consider your wireless handset or cell phone. Your wireless phone does have a limited range, but sensitive receivers can home in on the transmission from far enough away that you won't be able to see an obvious connection. They could be parked out of sight, just down the block. Your cell phone is even easier to crack. At a routing point within the web of towers and relay stations that comprises your phone service, computers could be looking for any traffic to or from your phone. All it takes is an approved order for a wiretap. Most wiretaps are issued for surveillance of cell phone use.

Not only phone conversations are at risk. Software can be downloaded to your cell phone without your knowing it, allowing it to be activated by observers and become a live microphone listening to your ordinary conversations. Phones that do things you haven't told them to do, or phones that turn on when there's no incoming call, could be signaling that there's a problem.

Legally the only people who could be doing this are supposed to be upholding the law and controlled by the court system, so if you're on the right side of things you shouldn't have reason to worry. But, you do. The same software the FBI uses to legally tap cell phones is available illegally over the internet, with instructions anyone can follow. Although it's a felony to use these programs, some people think it's worth the risk. Legal programs are less sophisticated but if someone has physical access to your phone they allow downloading of all data stored on your cell, including the restoration of deleted files. Sim Card readers make hacking into cell phones simple, but not ethical.

Wireless routing systems for your home computer also put your information at risk, including any phone conversations that go out over the internet on services such as Skype. Wireless networks have a typical useful range of 300 feet, meaning that in most cases the signal extends well beyond the user's house or apartment. The signal should be encrypted, but the older WEP system is easily cracked. The more secure WPA or WPA-2 encryption may not be compatible with older equipment or software. Using simple passwords easily matched by password trial and error programs will defeat the effectiveness of either one -- a randomly generated key sequence stored on a flash drive or flash memory card is a much better approach to password security. Even better, hardwire your system with LAN cables and password protect your PC's. The old LAN system is reliable and much less vulnerable.

Even such a simple thing as a wireless baby monitor for a child's room can broadcast beyond the walls of your home.

Disreputable home security services cater to the paranoid. Security experts may play on unwarranted fears by promoting a number of electronic devices that were either designed to detect obsolete systems or to do nothing but flash pretty lights at the uneducated but worried customer.

One of the most common gimmicks for sale pretends to detect listening devices that may be monitoring your calls. These are designed for home security checks and not for cell phones. Based on an observable effect -- the drop in voltage that signals another listening device on your line -- these detectors are not able to warn of more sensitive devices with better pickups, or of monitoring devices farther into the innards of the phone company than your house. If someone picks up a phone in another room while you're on the line, this detector will let you know. You'll probably also hear them pick up the phone.

Gimmicks designed to create a simulation of voice traffic on your phone line and fill up voice activated monitors with useless noise may actually be doing something, but whether it's actually useful in an era when data storage is unlimited is an easy call. The answer is no.

Black boxes which are supposedly able to deactivate any taps on the line, or scramble the signals of transmitter bugs by shifting their oscillation frequencies, are almost certainly frauds. I say almost certainly because there's a remote possibility that alien artifacts from the Roswell Crash might do this. If you believe that, you'd probably buy the black box. There are several real problems with the black box operation theory -- you can't affect an oscillation frequency by transmitting a signal unless the receiving device was designed to work that way, and the same goes for turning one off. A smart designer has no reason to add this flaw to the armor.

Something that is real, however, is a simple transmission detector. Knowing the general range of RF frequencies that bugs planted in an office or home may use allows scanning the area for unexplained signals in that range. Anything with the frequency band the detector scans will show up and by following the signal strength changes the device can be physically located. To turn the bug off, you'll have to step on it. There's no magic button on the detector for that, which is another sign that it's actually doing something. You've seen this gizmo on The Sopranos and on The Shield, but if you watch either series you'll notice that the other gimmicks never made it to prime time. They don't work. Tony Soprano would be very upset if you sold him one.

Reputable security firms know this. Real inspections involve getting dirty and looking into places people don't normally go. If your consultant works only by pressing mysterious buttons and doesn't check in the crawl space or the attic, it may be time for small claims court.

On one of the stranger forums I've visited, someone posted a question about a strange event. There had been a problem with her television. Instead of her favorite shows, one channel had begun displaying a page of technical data which she could not decipher. The technician who had fixed the problem made this cryptic comment about it: Hmm. You shouldn't be able to see that. The assumption she made was that it was forbidden, secret and sinister information that the public shouldn't have. After the technician did his work, she couldn't find that data channel any more.

Actually, it was cross talk. The tuner section was receiving the wrong channel, one which provided technical information that's of no importance to anyone who isn't setting up the satellite dish. It happens. Things get bumped, and especially in households with small children and people who try to fix things by magic hammer, controls get turned. Yes, you shouldn't be able to see that when you're trying to watch a rerun of your favorite MASH episode. It's boring and you wouldn't like it, but it is not sinister or forbidden.

Cross talk in electronic systems is common. If you hear strange voices when you pick up your phone, it's probably not the agents chatting in the surveillance van. It can happen because neighboring wireless phones happen to be set to the same frequency and their transmission zones overlap. It can happen because two cables lying side by side have faulty shielding. It may not even be an electronic issue -- the people who just rang your number might work in a call center and didn't notice the automatic dialer actually got a human response. Report recurring cross talk to the phone company. They will fix it.

Most strange electronic problems have very ordinary explanations easily resolved by competent technicians. Don't worry excessively about imperfections, like static on the line. It isn't hostile, just irritating.

If an expert is listening uninvited, you'll probably never know. Enjoy your blissful ignorance. Now and then say something nice about the government. Remark on how good a job the President is doing, and mention how wonderful it is to live in America. And don't do your banking on your cell phone.