Reverse addressed linear encoder?

Hello Forum,

I was hoping you might be able to resolve our quest to find a small ‘addressed’ chip/device that can show us location (on one axis) based on the return data of the chip address.

Basically, we have been looking for an ‘addressed’ hall effect device/chip (or similar) that can be placed at intervals within a 4 metre tube/pipe that is sealed against water ingress.
On the outside of the tube, a magnet in the damp environment would pass along the outside of this tube and hence affect the sensing operation of the closest hall effect chip in such a way that the ‘addressed’ device would send a signal to a CPU stating its unique address. In this way, the position of the magnet along the tube would be known by the returned address of the closest hall effect chip.

Alternatively, would a separate hall effect device (or even a magnetic reed switch) and separate ‘address sending device’ be available as a solution?