Sorry about that dangling preposition, but the saying is idiomatic -- correctly stated it would be: Here is another thing at which big dogs excel. Ponderous. And geeky. Anyway.
Big dogs make great alarm clocks.
Especially when the recalcitrant waker-upper in question has sneaked into our bed after we've gotten up and is very, very comfy and warm and not likely to budge on his own or at my request.
The reason they're such good alarm clocks? (Aside from the snorking and sniffling and shuffling around that they do?)
Big dogs do not have snooze buttons.