Problem testing for logged in users

I am trying to redirect a page if its URL is hit and there is no logged in user.

I have put various variations of the following into the lead template of a template layout stack, but it seems to be ignored.

{if logged_out}{redirect='...some other template...'}{/if}

I loaded up mo variables and tried using the early parsed variables that offers but got no better results - e.g. this doesn’t work:

{logged_in_member_id = '0'}{redirect='info/member-login-registration'}{/if}

I have checked and logged_in_member_id is reported as ‘0’ on the site when no user is logged in.

So I’m doing something dim, but not sure what.

Any guidance / suggestions would be most welcome 😊