diff --git a/checkpoint_manager.py b/checkpoint_manager.py
new file mode 100644
index 0000000..61ef7eb
--- /dev/null
+++ b/checkpoint_manager.py
@@ -0,0 +1,59 @@
+import pickle
+import os
+
+class CheckpointManager:
+    """
+    Encapsulate checkpoint functionality using pickle
+    """
+    
+    def __init__(self, filename: str):
+        """
+        Initialise with given filename
+
+        Args:
+            filename (str): Filename to use for saving/loading checkpoint
+        """
+        
+        self.filename = filename
+
+    def save(self, data):
+        """
+        Save data to checkpoint file with pickle
+
+        Args:
+            data: Object to be pickled
+        """
+        # mkdir if doesnt exist
+        directory = os.path.dirname(self.filename)
+        if directory and not os.path.exists(directory):
+            os.makedirs(directory, exist_ok=True)
+
+        # Save data
+        with open(self.filename, "wb") as f:
+            pickle.dump(data, f)
+        print(f"Checkpoint saved: {self.filename}")
+
+    def load(self):
+        """
+        Load and return data from checkpoint file .pkl
+
+        Returns:
+            Unpickled data object
+        """
+        if not os.path.exists(self.filename):
+            raise FileNotFoundError(f"Checkpoint file {self.filename} not found.")
+        with open(self.filename,"rb") as f:
+            data = pickle.load(f)
+        print(f"Checkpoint loaded: {self.filename}")
+
+        return data
+
+    def exists(self):
+        """
+        Check if the checkpoint file exists
+
+        Returns:
+            (bool) True if checkpoint exists, else False.
+        """
+        return os.path.exists(self.filename)
+
diff --git a/config.py b/config.py
index d2f5377..2cc550c 100644
--- a/config.py
+++ b/config.py
@@ -14,8 +14,10 @@
 CONDITIONS = ["pre_heat_exposure", "intra_heat_exposure", "post_heat_exposure"]
 
 # For checkpointing
-USE_CHECKPOINT = False
-CHECKPOINT_NAME = "processed_data.pkl"
+LOAD_CHECKPOINT = True
+SAVE_CHECKPOINT = False
+CHECKPOINT_FILE = "data/pickled/ID00_loaded_data_000.pkl"
+CHECKPOINT_ID = 0
 
 # Function to get participant directories
 def get_participant_dirs():
diff --git a/main.py b/main.py
index 20a0226..b6ef398 100644
--- a/main.py
+++ b/main.py
@@ -1,9 +1,27 @@
+import os
+
+from config import LOAD_CHECKPOINT, SAVE_CHECKPOINT, CHECKPOINT_ID,  CHECKPOINT_FILE
 from loader import load_all_participants
+from checkpoint_manager import CheckpointManager
 from preprocessor import merge_data, compute_sample_rate_for_sensor
 from visualiser import visualise_data_availability, plot_data_coverage_per_participant, plot_individual_participant_heatmap, visualise_ppg_ch0_minutes_stacked
+
 def main():
-    all_data = load_all_participants()
-    
+
+    checkpoint_mgr = CheckpointManager(CHECKPOINT_FILE)
+
+    # Data loading
+    if CHECKPOINT_ID == 0:
+        if LOAD_CHECKPOINT and checkpoint_mgr.exists():
+            # Load data from pickle file
+            all_data = checkpoint_mgr.load()
+        elif CHECKPOINT_ID == 0 and LOAD_CHECKPOINT == False:
+            # Load data from raw
+            all_data = load_all_participants()
+            if SAVE_CHECKPOINT:
+                checkpoint_mgr.save(all_data)
+        
+    breakpoint()    
     merged_data = {
         participant: {cat: merge_data(all_data[participant], cat) for cat in all_data[participant]}
         for participant in all_data
diff --git a/preprocessor.py b/preprocessor.py
index 4bbb33f..4d08573 100644
--- a/preprocessor.py
+++ b/preprocessor.py
@@ -2,7 +2,12 @@
 import numpy as np
 
 def merge_data(data: dict, category: str) -> dict:
-    """ Merge accelerometer, PPG, HR, and gyro data on sensor clock timestamps. """
+    """
+    Merge accelerometer, PPG, HR, and gyro data on sensor clock timestamps.
+    
+    Returns:
+        dict( subject_id{ condition{ pd.DataFrame}})
+    """
     if category not in data:
         print(f"Warning: Category '{category}' is missing.")
         return pd.DataFrame()
diff --git a/tests/test_checkpoint_manager.py b/tests/test_checkpoint_manager.py
new file mode 100644
index 0000000..2856f38
--- /dev/null
+++ b/tests/test_checkpoint_manager.py
@@ -0,0 +1,42 @@
+import os
+import tempfile
+import unittest
+from checkpoint_manager import CheckpointManager
+
+class TestCheckpointManager(unittest.TestCase):
+    def setUp(self):
+        temp = tempfile.NamedTemporaryFile(delete=False)
+        self.temp_file = temp.name
+        temp.close()
+
+        if os.path.exists(self.temp_file):
+            os.remove(self.temp_file)
+        self.checkpoint_mgr = CheckpointManager(self.temp_file)
+
+    def tearDown(self):
+        if os.path.exists(self.temp_file):
+            os.remove(self.temp_file)
+
+    def test_save_and_load(self):
+        data = {"key": "value", "numbers": [1,2,3]}
+        self.checkpoint_mgr.save(data)
+        loaded_data = self.checkpoint_mgr.load()
+        
+        self.assertEqual(data, loaded_data)
+
+    def test_exists(self):
+        self.assertFalse(self.checkpoint_mgr.exists())
+        data = {"test": 123}
+        self.checkpoint_mgr.save(data)
+        
+        self.assertTrue(self.checkpoint_mgr.exists())
+
+    def test_load_missing_file(self):
+        if os.path.exists(self.temp_file):
+            os.remove(self.temp_file)
+        
+        with self.assertRaises(FileNotFoundError):
+            self.checkpoint_mgr.load()
+
+if __name__ == "__main__":
+    unittest.main()