diff --git a/caimira/store/configuration.py b/caimira/store/configuration.py
index 155d80b2..bf7390ab 100644
--- a/caimira/store/configuration.py
+++ b/caimira/store/configuration.py
@@ -438,7 +438,7 @@ class Configuration:
             "activity": "Seated",
             "expiration": {"Breathing": 1, "Speaking": 9},
         },
-        "precise": {"activity": '', "expiration": {}},
+        "precise": {"activity": "", "expiration": {}},
     }
 
     def update(self, data):
diff --git a/caimira/store/data_service.py b/caimira/store/data_service.py
index e203be48..04fb5353 100644
--- a/caimira/store/data_service.py
+++ b/caimira/store/data_service.py
@@ -1,7 +1,9 @@
 import logging
 import os
 import typing
+from datetime import datetime, timedelta, timezone
 
+import jwt
 import requests
 
 from .configuration import config
@@ -24,12 +26,26 @@ class DataService:
         self._host = host
 
     def _is_valid(self, access_token):
-        # decode access_token
-        # check validity
+        try:
+            decoded = jwt.decode(
+                access_token, algorithms=["HS256"], options={"verify_signature": False}
+            )
+            expiration_timestamp = decoded["exp"]
+            expiration = datetime.utcfromtimestamp(expiration_timestamp).replace(
+                tzinfo=timezone.utc
+            )
+            now = datetime.now(timezone.utc)
+            return now < expiration - timedelta(
+                seconds=5
+            )  #  5 seconds time delta to avoid timing issues
+        except jwt.ExpiredSignatureError:
+            logger.warning("JWT token expired.")
+        except jwt.InvalidTokenError:
+            logger.warning("JWT token invalid.")
         return False
 
     def _login(self):
-        if self._is_valid(self._access_token):
+        if self._access_token and self._is_valid(self._access_token):
             return self._access_token
 
         # invalid access_token, fetch it again
diff --git a/caimira/tests/test_data_service.py b/caimira/tests/test_data_service.py
index 9e0189e7..e5740873 100644
--- a/caimira/tests/test_data_service.py
+++ b/caimira/tests/test_data_service.py
@@ -1,6 +1,9 @@
+import time
 import unittest
 from unittest.mock import Mock, patch
 
+import jwt
+
 from caimira.store.data_service import DataService
 
 
@@ -10,6 +13,24 @@ class DataServiceTests(unittest.TestCase):
         self.credentials = {"email": "test@example.com", "password": "password123"}
         self.data_service = DataService(self.credentials)
 
+    def test_jwt_expiration(self):
+        is_valid = self.data_service._is_valid(None)
+        self.assertFalse(is_valid)
+
+        now = time.time()
+
+        encoded = jwt.encode({"exp": now - 10}, "very secret", algorithm="HS256")
+        is_valid = self.data_service._is_valid(encoded)
+        self.assertFalse(is_valid)
+
+        encoded = jwt.encode({"exp": now}, "very secret", algorithm="HS256")
+        is_valid = self.data_service._is_valid(encoded)
+        self.assertFalse(is_valid)
+
+        encoded = jwt.encode({"exp": now + 10}, "very secret", algorithm="HS256")
+        is_valid = self.data_service._is_valid(encoded)
+        self.assertTrue(is_valid)
+
     @patch("requests.post")
     def test_login_successful(self, mock_post):
         # Mock successful login response
diff --git a/setup.py b/setup.py
index 41b69c1b..b8eb391d 100644
--- a/setup.py
+++ b/setup.py
@@ -30,6 +30,7 @@ REQUIREMENTS: dict = {
         'numpy',
         'pandas',
         'psutil',
+        'pyjwt',
         'python-dateutil',
         'retry',
         'scipy',