Hi- sorry for not replying earlier, although Mike has already done it.
Use AT for general location and IN for specific location:
He's AT home. He's IN the kichen.
PS I like your use of the word wary :lol:
Both "at" and "in" can be used for time and place. When used spatially "in" refers to the state of being "inside" as already said. with time expressions it refers to a period of time
In - Place: in my house
In - Time: in the morning
By contrast "at" doesn't really refer to the state of being "outside" but is a point in time or place:
At - Place: At the chemist's
At - Time. At 8 O'clock
"At" is a point for place or time. The commercial at @ is used because it is a meeting point. Since "at" is a point it is concerned with targeting and is often used with verbs that are aggressive in nature. Compare:
She shouted to me (not aggressive)
She shouted at me (aggressive)
He threw the ball to me (friendly)
He through the ball at me (aggressive)
Apart from that "at" and "in" can collocate with verbs or adjectives: as in:
Good at / bad at. It is interesting to see how English works in comparison with say German. It can see things as a point "at" or spatially "in". German by contrast is very spatial:
Gut in (good at)
Im Fernsehen (on TV).