All walkie-talkies feature the same basic components. Those include a speaker, microphone, battery, antenna, some circuitry and, of course, the iconic PTT button. These parts work in tandem to create useful radio signals.
Let's say you're whitewater rafting with a group of friends on a remote river, in an area where there's zero cell phone coverage. You depress the PTT button on your radio to chat with group members. As you speak, the walkie-talkie converts your voice into radio signals. Those signals are part of the electromagnetic spectrum, so they travel at the speed of light (186,000 miles, or 299,338 kilometers, per second) to all the other radios that are within range and on the same channel.
If you're not up to speed on radio technology basics, be sure to read How Radio Works. But in short, radios transmit and receive signals on any of millions of possible frequencies, which are denoted by units of Hertz (cycles per second). Those units are most often kilohertz (KHz) and megahertz (MHz). Modern, digital walkie-talkies may work on dozens of possible channels (or frequency bands), so in order to communicate with your buddies, you'll need to make sure you're all using the same channel before hitting the river.
All walkie-talkies are built to work on specific radio frequencies. In the United States, the primary frequencies designated for general public use are called Family Radio Service(FRS) and General Mobile Radio Service(GMRS). FRS or GMRS radios operate at frequencies in the 460-MHz range. The government also sets aside frequencies for corporate use, called Business Band, which includes frequencies between 450 and 470 MHz.
Frequencies are in finite supply, especially at the public level, so the airways are often jammed with too many signals at once, which can result in interference. As you'll soon read, many walkie-talkies come with features designed to filter out unwanted signals from other people. Still, radio signals often bounce around weirdly due to weather or other electromagnetic anomalies, which is why sometimes they pick up other signals inadvertently, such as in the West Virginia case of the baby monitor that spewed foul language from truckers talking on their CB radios [source: NBC News].
You'll learn more about how to filter signals later. For now, let's step back to the advent of walkie-talkies, and how they became so popular to begin with.