Do we have some value to depict the level of drowsiness or alertness?

We don't have specific drowsiness or fatigue detection yet, however, EMOTIV does provide access to frequency bands, both the frequency of the interaction and the specific location of the activity provide information about the kind of activity inside the brain. 

For example, Theta (4 - 8 Hz) activity is seen in drowsiness, arousal and often during meditation. Dominant Theta activity is associated with relaxed, meditative, and creative states, memory recall and 'flow' states. Alpha (8 - 12 Hz) are the default 'relaxed and alert' mode of the brain. High Alpha values are often observed in the rear channels (occipital and parietal sensors) when the eyes are closed, indicating that the visual processing system is not currently engaged but is available and waiting for input. Similar conditions apply to other parts of the brain. High Alpha levels appear in the frontal lobes during relaxation and are suppressed when other activities take place. It is quite common in EEG analysis to compare the Alpha suppression between different regions in order to determine the functional areas which are currently in use. For example, linguistic processing tends to depress Alpha activity in the left frontal lobe, while abstract spatial thinking can suppress Alpha in the right frontal lobe. Trained meditators often produce much higher levels of Alpha activity during normal activities, especially in the frontal lobes.