Synchronized diving - synchronizing tool allowed?

I know this isn't the US Masters Diving forum, but you're the closest thing I have to such a group. Is any sort of of synchronizing device allowed in synchronized diving? Like an earpiece beeping in sync for both divers like a metronome. Finis tempo trainer? If I had to guess, I'd guess, "no." Assuming not allowed in competition, do they use something like that in practice?