It's just a magnet that induces a current in the coil of wire that is the sesnor. The pulse of Alternating Current is what the computer is counting. So any magnet of sufficient strength to induce a detectable current would work.

What the computer is doing is a frequency=speed calculation. It has some version frequency counter, probably in conjunction with the clock crystal.
((pulse/time)*wheel circumference=rate) There's nothing fancy going on in there to screw up.

2 wheel magnets makes you twice a fast!