Warning: contains spoilers for Superman: Son of Kal-El Annual #1!
DC's Batman is an incredibly strong superhero (for a human without powers, unlike Superman) but his true strength is his stealth abilities. With years of training, he has mastered the art of sneaking through enemy strongholds - of allied domiciles - without being seen. This isn't always seen as a positive action, especially by his friends, and in Superman: Son of Kal-El Annual #1, the Dark Knight reveals the one place in the world where he can't pull off his classic stealth-surprise appearance.
In current DC comics continuity, Clark Kent has left Earth for parts unknown. He's left his son as the protector of the planet, and as the new Superman, Jonathan Kent struggles with following in his father's footsteps while also becoming his own man. Still, without his father's guidance, Jon occasionally feels lost, but Batman arrives with an item that will help: a Kryptonian memory crystal containing messages from his father. Unfortunately, Batman doesn't arrive in his traditional style.
While in his mother Lois Lane's apartment (the Kent house was destroyed in an explosion by a metahuman several issues previously) Superman hears the doorbell ring; he already knows who's waiting to enter (thanks to his X-ray vision), but he's nevertheless surprised. Opening the door, he greets Batman with "Batman knocks? I thought you'd just appear in our kitchen or something." Lois affirms that Batman did exactly that - but only once, and he'll never do it again. Lois apparently chastised him for appearing in her own home without announcing his presence.
Batman's signature move - his disappearing act - is often used to great effect on criminals and supervillains, but he uses it on allies as well, most notably Commissioner Gordon (beginning in Detective Comics #424 and continuing to this day). Not using the technique on Lois shows Batman actually respects not only boundaries, but certain people too. Despite their occasional animosity, Batman and Superman are still good friends, so much so that Lois knows Batman is secretly Bruce Wayne. This is a secret very few non-superheroes actually know; Batman's well-known trust issues mean that the people he does trust are few and far between.
Batman has occasionally been portrayed as a dark, brooding character who rarely trusts anyone outside of his butler Alfred and the members of the Bat-Family. With this revelation, it's clear that Batman respects Clark's family in a way he rarely does with others. Superman's son is in good hands if Batman is keeping watch.