diff --git a/features/screen.py b/features/screen.py
index 92fcba0..e2e3d2c 100644
--- a/features/screen.py
+++ b/features/screen.py
@@ -30,3 +30,23 @@ def get_screen_data(usernames: Collection) -> pd.DataFrame:
     with db_engine.connect() as connection:
         df_screen = pd.read_sql(query_screen.statement, connection)
     return df_screen
+
+
+def identify_screen_sequence(df_screen: pd.DataFrame) -> pd.DataFrame:
+    # TODO Implement a method that identifies "interesting" sequences of screen statuses.
+    # The main one are:
+    # - OFF -> ON -> unlocked (a true phone unlock)
+    # - OFF -> ON -> OFF/locked (no unlocking, i.e. a screen status check)
+    # Consider that screen data is sometimes unreliable as shown in expl_screen.ipynb:
+    # "I have also seen off -> on -> unlocked (with 2 - locked missing)
+    #   and off -> locked -> on -> off -> locked (*again*)."
+    # Either clean the data beforehand or deal with these inconsistencies in this function.
+    pass
+
+
+def time_screen_sequence(df_screen: pd.DataFrame) -> pd.DataFrame:
+    # TODO Use the results of indentify_screen_sequence to calculate time statistics related to transitions.
+    # For example, from the two main sequences outlined above, the time of "real" phone usage can be calculated,
+    #   i.e. how long the screen was unlocked.
+    # Another example might be the average time between screen unlocks and/or screen status checks.
+    pass
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