Here's how you can enable or disable the option to get an alert if there is potentially suspicious activity in your Gmail account.
1. Go to Gmail and login.
2. Look for the very small Details link at the very bottom of the page.
3. Click the Details link.
4. Click the Change link next to Alert Preference.
5. You can choose one of these two options:
Show an alert for unusual activity
Never show an alert for unusual activity