In the release build of the Yabby LoRaWAN, the LED is operational from reset until the first sleep. Thereafter, it is disabled for power saving reasons.

After reset the following will be observed:

1. A single 1 second flash on reset.
2. An additional 10 seconds of the LED on, if a brownout is suspected. This happens if the total battery voltage is sampled at less than 4.65V - the open circuit voltage of 3 x flat Lithium 1.5V LiFeSe cells. Additionally, the batteries are loaded and the voltage is monitored. The device will not start if the loading drops the battery voltage below a total of 3.00V. The reason for this cautious approach to startup on low batteries is respect for the duty cycle restrictions - repeated resets could lead to repeated transmissions, and breaking of the duty cycle laws. The device will only boot once reasonably confident that the batteries can sustain operation for long enough to obey the duty cycle laws.
3. The device will attempt to join the networkif configured for OTAA. The LED will flash at 2Hz during this period (250ms on, 250ms off). The device may fail, and back off until the duty cycle restrictions allows it to retry (30-120 seconds, 3 tries). The LED will be off during the back-off time, but will flash again during the retry.
4. The device will then turn on the GPS. While attempting to get a fix, the GPS will flash at 1Hz (500ms on, 500ms off).
5. The device will then transmit the GPS fix. This will be another 2Hz flash for the duration of the transmission - which is effectively 2 short flashes.

If the config cable is plugged in, the LED will be on constantly. Once removed, if the settings have changed, the device will reset, and start the behavior described above. 

If a firmware update is incomplete, the LED will go on permanently. To complete the update, plug the cable in again and run the config app.