I am working on a UI for a robotics application that uses radio communication. There is a text field for each robot that normally displays battery voltage in the format 3.72 V.

Sometimes the radio communication link breaks, so we can not query the battery voltage. I want to indicate this to the user place of the battery voltage. I am trying to choose a message of around 5 characters for this purpose.

If the radio connection is lost, most operations with the robot will fail. Our initial design used N/A (not applicable / not available) in the field to indicate this, but in my opinion N/A connotes more of a "warning" condition than an "error" condition.

Aviation uses INOP to indicate subsystems of an aircraft that are inoperative, but this is probably less well-known.

The ideal message would:

  • Be a "call to action", telling the user they probably need to fix something
  • Indicate that the radio has failed as opposed to a generic "something's wrong"
  • Be well-known

Of course I can make the UI more spacious or use icons, but if there is a good short textual message it will be easier to implement.

  • 1
    NOSIG ?........
    – PhillipW
    Commented Dec 19, 2020 at 11:59
  • 1
    FAIL (4 characters) or ⋆FAIL (5 characters) would seem to indicate failure. Is there a reason why you haven't chosen that? Commented Dec 20, 2020 at 11:47

4 Answers 4


DOWN it's well known among internet users and somehow indicates that the radio connection is lost.


There are a few ways to do this better, I'll share 2 possible solutions.

If your users are comfortable with documentation or there is space beside the UI to indicate a legend, you can consider using error codes to describe the error, for example, Err1 = check battery Err2 = no signal ...

Otherwise, if your users are power users, they will be familiar with common acronyms, you can consider adapting an acronym, for instance, from this site: https://www.microwavejournal.com/articles/3062-acronyms-and-abbreviations-used-by-the-rf-microwave-industry

Although I tried searching within the link and not sure what to suggest since not enough context is given; you can consider using

!-WAN or X-WAN

as ! and X are often associated with negative/ not working.


LOS ("Loss Of Signal") might be a solution. That is probably what I would use in this case.


  1. Law of the sea.
  2. Length of stay.
  3. Line of scrimmage.
  4. Line of sight.
  5. Loss of signal.

Oxford English Dictionary, via https://www.lexico.com/en/definition/los


Why no flashing text that alternates between "RADIO" and "LOST"? You can hardly make it clearer and more straightforward. At the same time, the flashing shows that there is a malfunction that requires user intervention.

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