94391-ND (94391) is a grounding monitor created by Desco. This device has a “park snap” that prevents the device from sounding off audibly when you leave the work area. According to the datasheet, there is a “7mm and a 4mm Park Snap on each module.” Here is that snippet from the datasheet:
Erroneous Beeping
It is possible the unit may not need extra calibration when you hook it up to your grounding environment the first time, however, there are recommended troubleshooting steps documented if you do hear the system alarm when it appears nothing is incorrect. The datasheet does indicate “that if all the connections are secure, the base unit needs to be adjusted to compensate for a different human body model.” You can adjust this using the trim pot found under a small hole on the desired remote module.
You can also run through the calibration steps seen on page 2-3:
Last Resort
If none of the steps mentioned in the datasheet work, then you may have a case where you have a defective unit. Please contact us at Techs@digikey.com if you are concerned about the behavior of the system.