This setting is turned off by default. Enabling it with mobile push notifications can be useful.
Of course, expect a few false positives (usually when you’re logging in from new places).
While you’re there, check the other options too :)
A simple yet powerful feature that one might miss!
For this to work, you must install Synology's DS Finder on your mobile device (available for iOS and Android).
While you're on your LAN launch DS Finder on your mobile and let it find your DiskStation, login to it and turn on Push notification...