Can you put a parked “under construction” page up at homepage with no links?

I would like to know if it possible to put a parked “under construction” or other simple message up at my homepage without any links, except possibly the admin account link, so that no one can access the site while I am working on it? It seems like there should be a way to do this, or else maybe they should add this option. I know some other platforms allow this.

Thanks