Note that nobody can login to your iCloud account without knowing your AppleID and password. And if you use two factor authentication with your AppleID, they’d have to have access to one of your trusted devices as well.
Also, if someone tries to sign into your account from a device not linked to your account, you will get a notification that an unknown device tried to login. You will also see a similar notification whenever you get and successfully add a new device to your Appleid (all your other devices get a notification that your AppleID was used on a new device).
No, not until I "Played a sound", which played & put up a dialog on the Mac, then I was sent an email, within 2 seconds, which of course arrived on both my iPhone & Mac simultaneously, telling me I'd 'Played a sound'.
So, you can check the location without any notification, provided that's all you do.