diff --git a/lib/admin.php b/lib/admin.php
index dc34182..f2ce49d 100644
--- a/lib/admin.php
+++ b/lib/admin.php
@@ -40,7 +40,8 @@ function admin_add(string $login, string $password): int {
     $db = DB();
     $db->insert('admins', [
         'login' => $login,
-        'password' => salt_password($password)
+        'password' => salt_password($password),
+        'activity_ts' => 0
     ]);
     return $db->insertId();
 }
@@ -95,6 +96,8 @@ function admin_auth(string $login, string $password): bool {
         'ua' => $_SERVER['HTTP_USER_AGENT'] ?? '',
     ]);
 
+    $db->query("UPDATE admins SET activity_ts=? WHERE id=?", $time, $id);
+
     $AdminSession->id = $id;
     $AdminSession->login = $login;
     $AdminSession->makeCSRFSalt($salted_password);
@@ -127,9 +130,11 @@ function _admin_check(): void {
 
     $cookie = (string)$_COOKIE[ADMIN_COOKIE_NAME];
     $db = DB();
+    $time = time();
     $q = $db->query("SELECT
             admin_auth.id AS auth_id,
             admin_auth.admin_id AS id,
+            admins.activity_ts AS activity_ts,
             admins.password AS salted_password,
             admins.login AS login
         FROM admin_auth
@@ -147,6 +152,9 @@ function _admin_check(): void {
     $AdminSession->login = $info['login'];
     $AdminSession->authId = (int)$info['auth_id'];
     $AdminSession->makeCSRFSalt($info['salted_password']);
+
+    if ($time - $info['activity_ts'] > 15)
+        $db->query("UPDATE admins SET activity_ts=? WHERE id=?", $time, $AdminSession->id);
 }
 
 function _admin_set_cookie(string $token): void {