// System.updatesPending() example

SYSTEM_MODE(SEMI_AUTOMATIC);

void setup() {
  // When disabling updates by default, you must use either system
  // thread enabled or system mode SEMI_AUTOMATIC or MANUAL
  System.disableUpdates();

  // After setting the disable updates flag, it's safe to connect to
  // the cloud.
  Particle.connect();
}

bool isSafeToUpdate() {
  // ...
  return true;
}

void loop() {
  // NB: System.updatesPending() should only be used in a Product
  if (isSafeToUpdate() && System.updatesPending()) {
        System.enableUpdates();

        // Wait 2 minutes for the update to complete and the device
        // to restart. If the device doesn't automatically reset, manually
        // reset just in case.
        unsigned long start = millis();
        while (millis() - start < (120 * 1000)) {
            Particle.process();
        }
        // You normally won't reach this point as the device will
        // restart automatically to apply the update.
        System.reset();
    }
    else {
      // ... do some critical activity that shouldn't be interrupted
    }
}

System.updatesPending() indicates if there is a firmware update pending that was not delivered to the device while updates were disabled. When an update is pending, the firmware_update_pending system event is emitted and the System.updatesPending() function returns true.

When new product firmware is released with the intelligent option enabled, the firmware is delivered immediately after release for devices that have firmware updates are enabled.

For devices with updates disabled, firmware updates are deferred by the device. The device is notified of the pending update at the time of deferral. The system event firmware_update_pending is emmitted and the System.updatesPending() function returns true. The update is delivered when the application later re-enables updates by calling System.enableUpdates(), or when updates are force enabled from the cloud, or when the device is restarted.

In addition, a cloud-side system event will be emitted when a pending OTA update is queued, particle/device/updates/pending with a data value of true.