A very common query here is; My Garmin product came with only one magnet and I need two. One for the spoke to pickup speed and the other for the crank to pickup my Cadence.
The answer is that the package actually does come with two magnets, but at first glance it looks like just one has been supplied. This is because in the packing of the magnets they are almost always joined through magnetism.
Some pictures below explain how they are packaged and what actually is supplied.
On the left is the packet of Garmin magnets with the speed magnet and cadence magnet stuck together.
The picture to the right shows the magnets separated and the spoke magnet screwed to the plastic retainer.
Same again, this time the Cateye magnets are pictured.