Reed sensors have a low stable ON resistance, typically only 50 to 100 milli-ohms. Hall sensors have the resistance of semiconductor material and generally runs in the 1000s of ohms. Electromechanical sensors have a low ON resistance, typically in the 50 to 100 milli-ohm range. However, they generally will pick up a film on the contacts with usage, and unless its burned off by switching a relatively high voltage and or current, its ON resistance will increase. It could be at the 1000s of ohms level across the contacts. If users are only switching low voltages or low signals, they may be lost going through the high contact ON resistance.