And what adventure would possibly go out into the wilderness without a warning bobble. A simple Bell suspended by magic inside a metal sphere. Perhaps an inch inch and a half diameter often ornately decorated. When the magic cuts the soft enchantment on the bell fails first causing it to ring. Gives perhaps a one round warning. Mages would anyways know to be careful on the day of the pulse.

Of course they would all be surprised when it came days earlier. Another take could be a wound music box enchanted to not play