With Raditz's arrival on Earth, Dragon Ball Z's debut episode introduces its viewers to the alien race known as the Saiyans, laying the foundations for Goku's wild journey to the afterlife and back again. It also debuts a less talked about but crucial piece of technology for its time: the scouter.
Fans traditionally associate the scouter with the early Saiyan, Namek and Frieza sagas as most of the villains from that time wore them. But the scouter has also appeared in later DBZ and Super films and video games, and the concept of measuring a fighter's power continued in later story arcs. Let's look at some history behind the scouter's usage as well as some interesting connections to modern-day technology.
According to a 2014 interview with Dragon Ball creator Akira Toriyama, the scouter was invented by the Tuffle race on Planet Vegeta as a defense mechanism. It was later modified by Frieza's engineer Gichamu to read exact power levels and telecommunicate, thus turning it into a more offensive weapon. This is disputed, however, by the Dragon Ball Super: Broly film which lists another Frieza Force engineer named Kikono as the scouter's inventor.
The scouter's most basic function is simple: to measure a fighter's power level, or ki. If the level is high enough, it also allows the user to get a general idea of that person's location. Using this function, Raditz was quickly able to find Goku at the secluded Kame House. When the Ginyu Force arrived on Namek, they brought a more advanced model that directly revealed a person's location along with their power level. These were widely used by many alien races, especially those in Frieza's army as they located suitable planets and wiped out their defenses before selling them in the planet trade.
That said, scouters aren't infallible and villains often learned the hard way not to rely on them completely. For example, they couldn't track when a Z fighter was hiding their true ki level. Vegeta discovered this flaw while battling Goku on Earth but later used the same exploit to his advantage on Namek in fights against Cui and Dodoria, who were too dependent on their scouters. In the Cooler's Revenge film, scouters were revealed to also be limited by height when Gohan and Icarus fly safely through the clouds to get past Cooler's minions. More recently, fans learned that scouters cannot measure God-level ki -- whether that's because it is a different type of energy or is simply too powerful is unknown.
The last time a traditional scouter is used in Dragon Ball Z is during the Trunks Saga, when King Cold's soldier measures Trunks' power as being at "Level 5." However, scouters and the general idea of measuring a fighter's power continue in the series to this day. In the World Tournament Saga, Babidi's henchmen Spopovich and Yamu use a weapon that measures the other fighters' abilities and absorbs their energy. In Dragon Ball Super: Broly, despite Frieza's soldiers using more advanced scouters, they still couldn't measure Broly's power level as it was too high to even register.
Although the scouters have long served an important purpose in the Dragon Ball series, it's also fortunate that they have their flaws and limitations. After all, if they worked perfectly, the outcome of every battle would be known before it even began. Luckily, these flaws allow for suspense and excitement to be at the fore of every fight.
As with plenty of other aspects of the Dragon Ball franchise, the scouter has connections to modern-day pop culture, not least in the conceptual design for Google Glass. Both devices are worn over the eyes, record information for the user, and operate with the help of a touchpad. Tech-savvy Reddit users have developed apps that use Glass to take a photo of a group of people and then measure their "power levels" through a special algorithm. CollegeHumor referenced the scouter in a video asking whether Glass would catch on in modern-day society.
And who can possibly forget the scouter-inspired phenomenon "It's Over 9000!!" - a three-word phrase that spawned countless t-shirts, memes and even a book about dealing with differing worldviews in modern culture. Not too shabby for a defunct little device.