Not sure what year your WRX is but my my suggestion would be "cup holders". And I don't mean "leave it in a cup holder"--pop the boot off the hand brake and there's like one screw and some clips to remove the cup holders from the center console and then an absolute _ton_ of space underneath. Even if someone _was_ looking there, there's room to hide it (hell, it's carpeted so a discreet hole in the carpet could hide it well).
If you put it towards the back near the center console storage, even with a phone someone's going to be checking the cup holders, the center console storage, down beside the seats, the seat back pockets, under the seats, _in the seats_, etc first. Then rechecking them. Then checking them again. Like you say, those would all be "normal" places to put it or drop it.
But you'll be able to pull it out and replace the battery or something in like 20 minutes when you had to do it once a year with nothing but a phillips screwdriver.
Alternatively, if you don't mind listening to it rattle around sometimes, from what I hear from people who have dropped rings and things into the under seat vents... you basically need to remove the entire interior to get in there. I'd get the 10 year battery first though.
If you put it towards the back near the center console storage, even with a phone someone's going to be checking the cup holders, the center console storage, down beside the seats, the seat back pockets, under the seats, _in the seats_, etc first. Then rechecking them. Then checking them again. Like you say, those would all be "normal" places to put it or drop it.
But you'll be able to pull it out and replace the battery or something in like 20 minutes when you had to do it once a year with nothing but a phillips screwdriver.
Alternatively, if you don't mind listening to it rattle around sometimes, from what I hear from people who have dropped rings and things into the under seat vents... you basically need to remove the entire interior to get in there. I'd get the 10 year battery first though.