How WiFi Detectors Work

A wireless signal can travel only so far. Specifically, a typic­al signal can extend as far as 1,000 feet (304.8 meters) in an unobstructed, open area and about 300 feet (91.44 meters) in a closed area that has obstructions [source: Graves]. Because the signals themselves are invisible and the access points (routers) that emit them are usually hidden, a WiFi detector can be a handy tool. WiFi detectors are basically just gadgets that can quickly and easily tell you whether you're around a WiFi signal.

Before we can understand the mechanics of WiFi detectors, let's take a quick look at wireless Internet. Although wireless Internet travels in waves similar to radio waves, it travels on very different frequencies. It actually travels on frequencies significantly higher than those of other common devices, such as cell phones. These frequencies that carry wireless Internet fall into the ranges of 2.4 GHz or 5 GHz, depending on the standard used.

In order to standardize the wireless Internet process, a group called the Institute of Electrical and Electronics Engineers (IEEE) has specified 802.11 as the group of networking standards it uses. Such standards specify how data travels through the waves. Different letter-signifiers further specify the set of standards. Some common ones are 802.11b and 802.11g, both of which use the 2.4-GHz band. Within the 2.4-GHz band, you have specific channels. In the United States, wireless Internet has 11 available channels on the 2.4-GHz band (other countries may have fewer or as many as 14).

The detector's job is to pick up on the waves with frequencies meant for transmitting wireless Internet. To accomplish this task, the antenna must be designed to receive the right kind of signals. Much like the antenna on your car radio is tuned to pick up on a specific range of frequencies (and not, say, frequencies that carry police communications), the antenna on a WiFi detector is tuned to pick up only on the specific band that carries wireless Internet. If you examine the specifics of detectors, many will list that they're meant for picking up 802.11b and 802.11g networks.

Antennas alone, however, wouldn't make very useful travel gadgets. A detector must have some sort of interface for alerting you when it does pick up on the right signals. Many will also gauge just how strong the signal is and convey that to you. In addition, many modern WiFi detectors also come with processers that allow them to demodulate (or process) the data to give you some valuable information before you decide to set up camp with your laptop.

As we mentioned, all WiFi detectors have interfaces that somehow inform you if a wireless signal is present. Apart from this basic function, however, all detectors are different. Manufacturers have come up with many methods for conveying the information to the user, and some of these gadgets are able to provide more information than others.

Many use LED lights, for instance. These typically light up in a scale fashion, where a single light indicates a weak signal, and more light up in sequence as the signal gets stronger. More advanced detectors use an LCD screen to display some useful information. Not only will it tell you the degree of signal strength, but perhaps also the SSID (Service Set Identifier), which is basically the name of the network. This would alert you to whether the wireless signal it's picking up is coming from your own home network or the neighbor's.

Detectors might also list the operating channel on which the network is working. This is helpful for reducing interference. It turns out that multiple networks working within the same proximity in the 2.4-GHz band can cause interference for each other. If you remember from the previous page, the 2.4-GHz band has 11 available channels in the United States. Interference can be reduced by spreading WiFi networks farther apart across the channel numbers. Thus, if your detector informs you that your neighbor's network is using channel 6, tune your router to channel 1 or 11.

When using WiFi detectors, remember that they run on batteries (usually AAA), so don't leave them on when you're not using them. Many include an indicator of battery that lets you know if it's in need of a replacement soon. Some actually have different settings that allow you to control the battery consumption or let you plug into your computer's USB port to charge [source: Dickey].

­Another helpful feature is that some detectors can tell you if the signal is encrypted (secured). If it's encrypted, you'll need a password to use it. Unfortunately, some people who travel around looking for unencrypted wireless signals might use this feature against you. When you leave your network unencrypted, freeloaders might snoop into your Internet activities or perform illegal downloads (such as music sharing). Authorities looking for the perpetrators could trace these downloads to your network, and you could get wrapped up in legal frustrations even if they can't ultimately pin the fault on you. So, it's important to keep your wireless network secure and encrypted with password protection.

Overall, when you travel with a laptop, a WiFi detector can be one of the handiest travel gadgets to bring with you. You can even get a small keychain version to ensure you never leave home without it.