Miniature Meta: Sensory Nin and a little bit on Minato || Sidenote: As always, this is my interpretation. Yours may differ. Which is fine.
So...how does one sensor-ify? It is not a skill that can be learnt, per se. Some are simply borne with an innate sensitivity to different chakra frequencies.
That isn’t to say however, that those born without this sensitivity are unable to sense certain chakra signatures; it can be acquired through enough practice [such as meditation, mastery over Yin release, sage training] - in fact, experienced shinobi [Densetsu Sanin, Hatake Sakumo, certain Jōnin] are able to identify certain, lesser known wavelengths over a restricted peripheral.
I believe its roots lie in ninshū and ninjutsu. Why? Brace thyselves--
Ninshu is the ideology behind ninjutsu - to connect people spiritually, for the sake of understanding one another, peace and harmony. Ninshu stems from Hagoromo, though it got manipulated and abused into ninjutsu [because have you seen the number of conflicts and reincarnations? Shinobi = collectively thick headed] before Naruto’s talk no jutsu restored the balance somewhat. Not to say they don’t use ninjutsu anymore - the ideology is simply less corrosive because everyone is friends now.
Back to ninshu: the concept of sharing spiritual energies in order to connect with others foreshadows the sensory peripheral. Certain clans, such as the Uzumaki, inherited this aspect from the source itself whereas other clans - such as the Yamanaka, probably acquired it early on and managed to nurture [yay inbreeding] it to the point of ‘sensory-ness’ being a clan specialty.
Important to note: Not every clansman manifests the trait in the same way, as evidenced by the fact that not every Uzumaki or Senju [sole exception being Tobirama so far] is born with the innate skill. The nuance of being able to ‘sense’ emotions/chakra/auras could apply differently. The same stands for other clans in other regions who manage to ‘sense’ different aspects. That however, is a conversation for another meta.
Chakra and energies rely on certain signatures - wavelengths, if you will. [evidenced by Nagato controlling several bodies via rods] Naturally, since every chakra signature involves certain wavelengths, a sensor type would have to actively switch to receptor mode so as to open all the channels, in a manner of speaking [kinda like a nifty human antenna]. The Yamanaka were quite adept at it.
Yin release ties into this because it deals with spiritual energy and the subconscious/unconscious. It isn’t explored in the manga as much, but I’ve exchanged a word or two with @senjutsunade about how Tsunade’s mastery over Yin release [as evidenced by her byakugo seal] makes her better at sensing certain energies - the trait would manifest in Sakura likewise. Perhaps not as skilled as an innate sensor type, but better than most others [though I believe sage training would make them just as adept as a sensor, probably even better].
Speaking of senjutsu and the sage realm -- tis one that relies on natural energies irrespective of chakra. The sensory range of a sage far out-strips that of an innate sensor - they can sense ‘life’, irrespective of chakra wavelengths over a wide spectrum. That would explain why sages and certain summons can track/trace/be inherently aware of their surroundings. By certain summons, I would like to refer to Kakashi’s Inue spirits in particular - they are not exactly dogs, per se, but they are excellent trackers [the inue symbolism thingus is an added bonus]. I’ve bugged @konohagakurekakashi about it quite a bit and there’s an interesting little detail they chalked out: his summons aren’t entirely dependent on scent, as they are on lingering strands of natural/spiritual energy. They are more spiritually aware of their surroundings and that in itself, makes them superior trackers.
Additional note: Taoism could be considered a very loose signifier with regards to senjutsu as a signified, but if I were to start on that, this post would turn into a freaking chapter. Er...another post, maybe? [Unless you want a crash course on Saussure and the Taoist narrative @@ Maa...]
On to Minato: I’ve already tackled the bit about him being a sensor in this post. His fighting style is wholly dependent on the fact. [Here I repeat myself] Minato is an excellent sensor, as evidenced by the manga [239]. His sensory peripheral extends to a wide radius, and if he had had enough time to master senjutsu, it would have complimented his adaption of the Hiraishin to a devastating degree.
Though...senjutsu would make him ridiculously OP [insert dismissive hand wave gesture] lets just pause here and leave Minato as the sneaky little bastard that he is. Here’s an excerpt [appendix A] from a history scroll I made up:
Advantages: A tactical upper-hand. This can be elucidated in Minato and Tobirama’s battle tact, as observed in the Fourth Shinobi War. Also, lets not forget the fact that Ino managed to telepathically connect everyone because she was an exemplary sensor - her skills lay in telepathy and projection, whereas the dead kages were more inclined towards instant execution. [Hiraishin does that to people]
Disadvantages: Increased sensitivity which may leave an inexperienced sensory nin vulnerable. There is something called sensory overload, which would make...sense [badum ts] in this scenario.
Personal headcanon: Minato, in particular, has trouble holding his liquor in the early days - primarily because too much of it makes him acutely sensitive to the various frequencies littered around his sensory peripheral. He could be described as the ‘passed-out’ drunk [something his fellow Jonin have yet to let him forget]. This reaction gets better with experience, as the ‘switch’ to sensory mode becomes more defined, more...controlled, in a manner of speaking. ‘Tis ninja science!
Also, he’s a lightweight because I find it hilarious. ^^ Its the perfect chink in the armor for well meaning [cough] comrades to exploit. Makes him more human -- demo, feel free to disagree. I am but a humble blog with nary a point to prove.
P.s. The Shippuden manga is my primary source of information. The anime is secondary and therefore, unsavory. I did however, consult Narutopedia - but only because it has an interesting note on the script - the hiragana used for ‘senjutsu’ and ‘sensory’. The links for Yin, Ninshuu and Ninjutsu have been included for a basic understanding.
Further P.s. My metas/headcanons have a habit of attracting anon ire. Apologies if this post offends you in any way or form - ‘twas not intended.