Honeywell SS311PT Hall sensor
The SS311PT/SS411P digital Hall-effect sensors are operated by a magnetic field and designed to respond to alternating North and South poles.
They can be powered between 2.7 Vdc to 7 Vdc.
The output is open collector but has an integrated 10 kOhm pull-up resistor.
The sensor connectors are located in the I/O board's middle row.