Neptune Systems

MOS Magnetic Optical Sensor

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Modern & compact magnetic water level monitoring

  • Improved look, feel, and design 
  • Precise water level control
  • Built-in magnetic mount
  • Silicone-encased external magnet
  • Completely waterproof
  • Compact form factor fits into tight spaces
  • Strong magnetic mount suitable for glass or acrylic up to 1/2" thick


The Neptune MOS replaces the previous OS-1-M and features an updated design that fits into tighter spaces and helps to prevent water incursion into the sensor. The MOS plugs into an Apex FMM port and uses reflected infrared light to signal your Apex when it changes state from being wet to dry or dry to wet. This sensor can be used for constructing your own ATO (auto-top-off), as a high-level warning sensor in your sump, water storage level sensor, and much more. The sensors can be mounted on any type of reservoir that has up to 1/4" thick walls. 


More Information
UPC 653078004991
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Product Questions

Is there an extension cord available for the Neptune MOS? I would need to run the cable another 10 feet to a remote saltwater bin.

Thank you.
Question by: Christopher Hill on Mar 10, 2023, 2:29 PM
Thanks for the question! At this time there are no Neptune authorized extension cables. for this application, we'd recommend installing the FMM closer to the bin and doing an AquaBus extension instead.
Answer by: Kyle Thomas (BRS Staff) on Apr 27, 2023, 3:37 PM
How long is thew cable?
Question by: Benoit Martin on Feb 12, 2023, 2:21 PM
this cable will be 5 meters.
Answer by: William Reed (BRS Staff) on Mar 16, 2023, 10:13 AM