Unfortunately, you cannot create a rule within MyGeotab for the absence of data. However, you can customize the Watchdog Report and change the SendReport flag within the Data sheet to depend on a formula.The Data sheet is hidden by default within the MyGeotab report so as a first step you will have to temporarily unhide this sheet.
The criteria you use to send the report will depend on what your requirements however as an example you could use something like: =IF(SUM(Report!B13:15)>0,True,False).
The above formula will look if there are any devices flagged as not communicating in the Report sheet, see screenshot below:
Once this is completed, save the excel file and re-upload it into MyGeotab. This way when the GO device is not transmitting data, the customer will receive an e-mail with the watchdog report.