Late but...
I just spotted an omnipolar Hall effect ic from Rohm. Has two outputs that =
could probably be diode anded. One for each magnet polarity.
BU52075GWZ-E2
https://www.mouser.com/search/refine.aspx?Ntk=3DP_MarCom&Ntt=3D145692848
Draws 5uA
$.48 for one $.20ea for 100
Looking forward,
Al Shinn (Tinker)

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