Android 17 and Android 18 were created by Red Ribbon Army’s Dr Gero. The main purpose of their creation was to avenge their creator’s vendetta against Goku, who single-handedly took down the Red Ribbon Army. The duo were initially human beings who had their body genetically modified into cyborgs. The fact that they possess an unlimited energy supply is well known, but can they also sense Ki?
Android 17 and 18’s respective original names are Lapis and Lazuli. Unlike Android 19 and 20, they cannot absorb the energy of their opponents.
Can Android 17 and 18’s energy be sensed?
No. Since Android 17 and 18 lack a Ki signature, they cannot be sensed via Ki sense or scouters. This feature along with their unlimited energy supply makes them challenging opponents to fight.
Can Android 17 and 18 sense Ki?
In Dragon Ball manga chapter 362, during the confrontation between Cell and Piccolo – Android 17 asked Android 16 to use his power reader to identify what was happening. Similarly, in Dragon Ball Super manga chapter 36, Android 17 states that he cannot sense Ki.
These two instances clearly make it seem that Android 17 and 18 cannot sense Ki.
However on the other hand, during the Buu Saga, Android 18 was able to sense the Ki of Majin Buu. This instance is only in the anime, so you could classify it as anime filler.
It’s interesting to note that characters can learn to sense Ki through training. Vegeta mastered it during his short time on earth while Videl learnt it from Gohan. So it’s plausible that Android 18 learnt how to sense Ki from Krillin. Still, this is a mere assumption or head cannon if you want to call it. As far as proof goes, there is more evidence that Android 17 and 18 cannot sense Ki.