Ted smiles, touched by Sherlock's actions. That's actually very reassuring, to know she has someone looking out for her, making sure she's safe. And from what she says, Sherlock is very good at his job, and cares about her a lot, so obviously he'd take that seriously.

"Remind me to thank him," he says softly. It's still wild to him that this sort of thing can be discussed so casually, but this piece of information does a lot to soothe his worry.