Hi,
as stated in the documentation measurements always require to have numerical values. You could extend a measurement and provide additional information by using custom fragments. But these custom fragments won’t be picked up by any of the Cumulocity built-in components. In addition, I don’t think it would be the correct approach for your requirements.
The information you want to send to Cumulocity for your device is describing a state of change for the device. For example, if the device is out of range or whether the device is on/off. For such kind of information you typically use Events in Cumulocity. Link to predefined MQTT templates. Next to the Measurement tab in Cumulocity’s Device Management application you have an Events tab, which displays all received events. There is also a widget for the dashboard to display received events in a list.
If you want to visualize your events differently than just as a plain list, you need to implement your own plugin or widget. There is also the Process Widget from Global PreSales you might want to look into.
Best regards
Christian