How do scouters work?

[LiamKav]

Obviously the Saiyans don't care about health and safety regulations.

[CaBrPi]

I remember when I was first reading Dragonball how shocked I was to hear Goku talk about him sensing the villagers in the town Oolong was terrorizing. Did that town have a specific name? And there are just multiple accounts of things that sound like ki sensing , even though they weren't supposed to really have this ability yet.

I always chalked that one up to Goku's superhuman senses, especially smell.

[dbzfan7]

I guess they pick up ki that is expelled from a persons body, kinda like how Goku naturally feels the flow of ki, the scouters do the same thing and put a number of how much ki is being put out.

[Fox666]

I remember when I was first reading Dragonball how shocked I was to hear Goku talk about him sensing the villagers in the town Oolong was terrorizing. Did that town have a specific name? And there are just multiple accounts of things that sound like ki sensing , even though they weren't supposed to really have this ability yet.

I always chalked that one up to Goku's superhuman senses, especially smell.

I dunno, Vegeta also said something about sensing Kuririn or Gohan presence when he was an Oozaru. There is also Freeza dodging a Kienzan from behind... this is not Ki, but still is some extra-sensorial ability.

[CaBrPi]

There's also Popo teaching Goku to sense the presence of others by feeling the minute changes in air currents.

[matt0044]

I remember when I was first reading Dragonball how shocked I was to hear Goku talk about him sensing the villagers in the town Oolong was terrorizing. Did that town have a specific name? And there are just multiple accounts of things that sound like ki sensing , even though they weren't supposed to really have this ability yet.

He could sense there presence.

[Mjb1985]

Are you saying sensing their prescense and sensing their ki is different ?

[Super Saiyan Turlast x4]

Pretty much. Goku was able to sense that there were people there, but that's the extent of it.

Roshi also seemed to be impressed at General Blue's ability to hide his presence, which seemed to be more focused on his stealth ability rather than any type of Chi suppressing.

[matt0044]

Are you saying sensing their prescense and sensing their ki is different ?

Sensing one's presence is knowing somebody's location when they're trying to hide and sensing one's ki is knowing their strength or at least what they're not concealing.

[Mjb1985]

How come Dodoria can't sense Gohan / Kuririn presence?

[Super Saiyan Turlast x4]

Because Dodoria (along with the majority of Freeza's henchmen) were accustomed to relying on scouters for stuff like that. It's even stated that they simply relied on power far too much. Also, I don't think everyone is capable of sensing one's presence.

[Mjb1985]

What about Vegeta? Can he sense one's presence?

[Super Saiyan Turlast x4]

I guess that'd come down to your interpretation. Oozaru Vegeta basically says he was aware that Goku's friends were around, but he didn't know where exactly. Probably was just a hunch on his part. Then you have Yaji sneaking up on Vegeta twice and attacking him, so I'd probably say his ability to detect presences weren't anything special.

[Bussani]

"Sensing someone's presence" just means knowing someone's there because your senses say they are. Feeling someone's ki is a method of sensing their presence. Another method would be hearing their heartbeat, or feeling subtle movements in the air as they move.

[Mjb1985]

What about when Goku can tell that Grandpa Gohan was strong, or that Tenshinhan was strong?

[Bussani]

It could be ki sensing, but I'd be able to believe it was another instinct. In manga, with enough skill, you can tell someone's strong just by looking at them. It's like how Kuririn was able to tell that Cell was hiding his real strength after being hit by him, or how Goku and Karin could make educated guesses about how much power Cell had up his sleeve. Heck, even Ginyu was able to accurately guess how much power Goku was holding back, and he couldn't sense ki at all.

[Mjb1985]

That could be it. Because there is a ton of quotes where they seem to be ki sensing prior to them being able to truly sense ki.

[Ketchup_Revenge]

In all honesty, we don't even know the mechanics of ki flow or radiation, or anything of the sort, so I don't believe this question can be answered honestly.

The reason I don't think it has as much to do with amount is because Goku and Piccolo's levels both read differently when they removed their weights against Raditz. They didn't obtain more ki at that point, but the flow of it through their bodies had somehow changed. Same with the scouter going all haywire when they'd concentrated their ki attacks. The ki amount itself hadn't changed in their bodies, but the concentration of it in certain areas had. So if anything, the reading on a scouter could be a combination of amount, flow, and concentration.

Also there's the concept of "powering up". However, in the Viz translation, they simply state that it's "revving", which (if that's an accurate concept) that would simply mean that they're increasing the rate of flow and not actually obtaining more ki somehow. The same concept of consciously influencing ki flow could be used with suppression, but instead of increasing the flow, the person could simply be consciously hindering the flow so it reads lower on a scouter.

This "revving" vs "obtaining more ki" concept would also explain how the Kaioken is fundamentally different from simply "powering up". The Kaioken somehow multiplies the ki, something that Goku can't do through simply powering up (otherwise he would instead of risking his body being destroyed). This could also explain why there's a big gap in ki level between Super Saiyan and base states (or any other person with a transformation).
If base states (And Super Saiyan states) really do have a fixed ki, then the change in level while in those states comes from manipulating the concentration or flow of that ki, not by obtaining or getting rid of ki somehow.

EDIT: As for the whole "sensing presence" thing, I think it has more to do with instincts than it does with actually being able to sense ki. You can get a feeling from body language or changes in the environment, but does it mean you have to know how to sense ki? Probably not. "Ki Sensing" is a similar concept, but the ones who can do that are in a totally different league.