Ki Sense, also called Reading Ki, is an ability that allows the user to sense ki and power levels. It is used by a vast majority of the Z Fighters, and was first introduced in the King Piccolo Saga of the Dragon Ball anime.
Ki sensing is the ability to sense the location, life force, and power level of anyone; the stronger and closer the enemy, the more powerful the sensation. Also, if a ki is very powerful, it can be sensed from afar by people who are trained to sense energy; like Gohan sensing Super Saiyan 3 Goku's energy all the way from the Sacred World of the Kais. Once a fighter masters the skill, they can use it even when their other five senses are incapacitated.
No outsider knows the sensations associated with ki sensing, as Mr. Popo likens explaining it to someone as being like "describing sight to the blind." However, the manga and anime usually show a minor spark on their head to signify that the Z Fighter is picking up a power.
Despite how common the technique is in later sagas, and how easy it is to learn for an adept martial artist, it actually appears to be a rare ability, as the Galactic Frieza Army was unaware of the technique until they faced the Z Fighters. Frieza and his army, who did not possess this ability, use a device called a scouter that can give numerical readings of a person's location and power level. However, scouters have been shown to be very fragile, breaking when a fighter powers up too much, making the ki sensing technique preferred for those who know how to use it.
Namekians are able to sense if the life force is good or evil; such as when the Ginyu Force arrived on Namek: Krillin senses their presence and thinks it is Goku, but Nail says "I, too, sense the presence of evil coming." The Namekian ki sense is displayed for the first time on-screen when Raditz approaches Piccolo on Earth: Piccolo reasons that the incoming power could not be Goku because "It's too horrible." Trained fighters also have the ability to sense whether or not a presence is good or evil, as Goku says "It's a horrible power, too! I'm trembling!" as he senses Raditz approaching Kame House, and later when he says that he senses evil when Black Smoke Shenron is summoned.
It appears as if each organism has a distinct ki signature, much like fingerprints in the real world. This is evidenced during Cell's introduction in the series, where the Z Fighters, prior to finding out who Cell was, described his ki signature as a combination of Goku's, Vegeta's, Piccolo's, Frieza's, and King Cold's ki signatures (the main components of Cell's biological makeup). Gods have a holy kind of ki that cannot be sensed by Humans nor Saiyans; such ki can also be obtained by becoming Super Saiyan God.
The Instant Transmission technique, requires the user to home in on a ki signature before teleporting them to that ki signatures location or somewhere nearby. Meaning the ability to sense ki is a requirement (the Instantaneous Movement technique however does not require a ki signature or the ability to sense ki).
- Goku – He first demonstrates the technique after drinking the Ultra Divine Water, but is only able to tell where King Piccolo is. After training under Mr. Popo, Goku is able to master the skill to the point where he is not worried about Tien Shinhan fighting Mercenary Tao because he knows Tien can beat him.
- Korin – He is able to sense ki. He senses Goku's increased energy by drinking the Ultra Divine Water, he senses the ki of those alive after the battle against Vegeta, and Goku visits and powered up in front Korin after his Hyperbolic Time Chamber training for Korin to sense his power level.
- Mr. Popo – He helps Goku, Krillin, Tien Shinhan, Yamcha, Chiaotzu, and Yajirobe master ki sensing.
- Piccolo – He demonstrates the ability several times in the series, notably to find Gohan and Frieza on Namek.
- Gohan – Learnt during his training with Piccolo.
- Krillin – Krillin displays the ability at the beginning of Dragon Ball Z, when he senses Raditz approaching the Kame house.
- Yamcha – Learnt with the help of Mr. Popo. He demonstrates the ability to sense ki during the arrival of the Saiyans on Earth.
- Tien Shinhan – Learnt with the help of Mr. Popo. He demonstrates the ability to sense ki during the arrival of the Saiyans on Earth.
- Chiaotzu – Learnt with the help of Mr. Popo. He demonstrates the ability to sense ki during the arrival of the Saiyans on Earth.
- Yajirobe – Also learnt with the help of Mr. Popo. He demonstrates the ability to sense ki twice during the Saiyan Saga: once (in the anime, only) to pinpoint the exact location of Vegeta and Nappa to journalists, and later when he comments on the immense ki of the Spirit Bomb.
- Vegeta – He had managed to learn this ability after his battle on Earth.
- Future Trunks – As shown when he sensed Cell powering up in Gingertown.
- Trunks – As shown when he sensed Goku and Majin Vegeta fighting while he was going to Babidi's spaceship with Goten.
- Goten – As shown when he sensed Goku and Majin Vegeta fighting while he was going to Babidi's spaceship with Trunks.
- Master Roshi – He is shown to possess this ability at various points in the series.
- Nail – As shown when he sensed the Ginyu Force arriving on Namek, and later Frieza heading to Grand Elder Guru's house.
- Dr. Wheelo – He is shown to be able to detect ki. It is unknown if this ability is natural or mechanical or a combination of both.
- Lord Slug – He was shown to be capable of this as he knew where Goku was hiding in their fight. Also, he was able to see Piccolo's energy inside of Goku.
- Cooler – Though Frieza and King Cold are unable to sense power levels without a scouter, Cooler can sense power levels (as it is required to use the Instant Transmission technique), as well as hide his own power level (allowing him to be able to sneak up opponents like Piccolo). The Meta-Coolers appear to be able to detect power levels likely through technological means.
- Some of the Red Ribbon Androids:
- Android 19 and Android 20/Dr. Gero – They have a device able to detect and analyze an opponent's power level much like a scouter.
- Android 16 – Although, Android 17 and Android 18 could not sense power levels, Android 16 had software in his design that worked much like a scouter. Android 18 may have later learned how to sense ki (maybe from her husband, Krillin).
- Android 13, Android 14, and Android 15 – They all possess ki sensing devices linked to Dr. Gero's Super Computer.
- Cell – As he possesses cells from various Z Fighters. Also, he uses this in order to perform the Instant Transmission technique while in his Super Perfect form.
- Super Buu and Kid Buu – While the fat Majin Buu did not possess this ability, Super Buu and Kid Buu did.
- Frieza – Frieza seems to possesses the ability in Dragon Ball GT, as he is shown to be amazed when he feels Goku powering up while in Hell. He also possesses this ability in the PSP game Dragon Ball Z: Shin Budokai, and is also shown to have learned how to hide his own power without using lesser forms as well.
- Broly – Daizenshuu 6 stated that Broly sensed Paragus trying to escape New Planet Vegeta. In Budokai Tenkaichi, during a random fight, Broly states that he notices an increase in his opponent's power level. In the story of Shin Budokai, while fighting against Gohan, Broly apparently senses Goku nearby and rushes off to fight him.