This is what the Status widget is for. It is a good idea to create a Status widget on your dashboard for each device referenced there. This will give a live, visible indication of how the device is working. Remember to set a sensible timeout, several times greater than the device's update rate. This is what the Status means:
It may also be a good idea to set up a warning Event to let you know if any particular warning/error comes to pass. The greater the number, the more concerning the error so setting the trigger as above 60 would let you know if the module reports an error (eg low batt) or loses communications with a module as well as if there have been no comms at all with the device since the heartbeat period elapsed.