Compact text indication of lost radio connection

Question

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.

Answer 1

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

Answer 2

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.

Answer 3

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

LOS

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}

Answer 4

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.