From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Dragon Radar (ドラゴン レーダー, Doragon Rēdā) was a tracking device designed and built by Bulma to help locate the Dragon Balls. This made finding the Dragon Balls more efficient compared to conventional methods. Dragon Balls emitted a faint electromagnetic pulse which the radar could detect. It then pointed arrows in the directions of nearby Dragon Balls. Pressing the button on the top would cause the view to zoom out and show more and more of the planet.
In Dragon Ball, Goku accidentally broke the Dragon Radar while fighting aganst Blue. During his search for a capable mind to fix the radar, Goku met Arale, from Dr. Slump, who asked her father/creator Senbei Norimaki to fix it. Senbei could not make heads nor tails of it. Turbo, her baby genius "brother", fixed it while nobody else was looking.
The radar is used frequently by Goku and his friends in Dragon Ball and Dragon Ball Z, but in Dragon Ball GT the Dragon Radar is assimilated by Gill and therefore they must use Gill's Dragon Radar (ギル の ドラゴン レーダー, Giru no Doragon Rēdā) to find the Black Star Dragon Balls.
Bulma's Dragon Radar is not the only device capable of locating Dragon Balls. Throughout the series, many other devices that work much the same way are also seen. One often seen is the Global Dragon Radar.
Red Ribbon Army
During their hunt for the Dragon Balls, the Red Ribbon Army had their own version of the Dragon Radar, but it was rather primitive and could only give a general idea of where the Dragon Balls were. Large groups of soldiers had to be dispatched to the location, resulting in many man-hours of backbreaking labor and invading of innocents' homes.
Pilaf eventually built his own, superior version of the Dragon Radar. It was shaped like a globe in order to minimize map distortion. It was installed in his floating airship, and was able to show the Dragon Balls' exact location on the planet.
Other Z Warriors radars
Along with the Dragon Radars invented by villains, the Z Warriors also had many different Dragon Radars. Although these Dragon Radars did not differ in form or function from one another, they were still different items. In fact, the Dragon Radar used in the majority of Dragon Ball Z is actually not the one Bulma introduced in "The Secret of the Dragon Balls" (that one is presumed to lie dormant in Dr. Slump's laboratory damaged beyond repair).
Turbo Norimaki created a new Dragon Radar for Goku when the old one was stolen by Blue.
In Dragon Ball Z: Fusion Reborn, Dragon Ball Z: Wrath of the Dragon, and the beginning of the Shadow Dragon Saga, the entire Z Warriors team split up into seven groups, each tasked with finding one Dragon Ball. It is presumed that Bulma made Dragon Radars for each of them otherwise they would not have been able to find the Dragon Balls so quickly.
Dragon Radar is collection item No. 6 in Dragon Ball: Advanced Adventure.
- There is an iPhone/iPod Touch application that emulates the Dragon Radar. It is named DRadar.
- The Dragon Radar in the live action South Korean film coincidentally resembled the DS series of Nintendo handhelds, as well as the Dual Screen Game and Watch handhelds.
- In "Rivals and Arrivals", the man running the registration for the Tenkaichi Tournament is looking at a clock that closely resembles the Dragon Radar.
- As stated by Bulma (Dragon Ball volume 1, chapter 1, pg. 25)