Hallway Smart Switch help
This is perfectly normal.   

This is a switch loop coming into switch 3.  

Ordinarily you would have a plain switch attached to the /2 cable's black and white (white should be marked with tape, since it is being used as either an always-hot or a switched-hot, you're supposed to use it for always-hot).  

A 3-way or 3/4-way complex simply substitutes for a plain switch.  That is what is happening here.  Red and white in the /3 cables are travelers; I would remark them with yellow tape.  The black is presumably always-hot. 

Now if you've been counting, here's what you have available in these boxes: 


always-hot (/3 black and presumably /2 white)
switched-hot (presumably /2 black)
Travelers (all other conductors)


Notice something missing? Neutral.  It will be hard to hook up a smart switch unless it is one of the few made and  UL listed to use ground instead of neutral.