But it's not a car.
Musk's tweet, which prompted a 3% rise in Tesla's stock value, said, "Major new Tesla product line -- not a car -- will be unveiled at our Hawthorne Design Studio on Thurs 8pm, April 30."
Musk has said previously that his company is working on a variety of electrical storage systems, among them systems that could gather and store power from solar panels -- perhaps solar panels made by one of Musk's other companies, Solar City.
Online pundits were quick to guess some such system would be the subject of Musk's April 30 presentation, as well as to suggest other comical possibilities. Among the Twitter suggestions: A Tesla hovercraft and a flying broom.
Musk's last Twitter tease didn't go so well.
Two weeks ago, the Tesla and SpaceX entrepreneur tweeted his intention to unveil a product that would put an end to "range anxiety," which is the fear drivers of electric vehicles have of running out of a juice before they reach a charging station.
Tesla stock fell several percentage points when the product Musk unveiled proved to be nothing more than a software update that would make it easier for Tesla owners to locate charging stations and calculate their chances of getting there.
A Tesla spokesperson declined to offer additional details on Monday's tweet, except to confirm the Hawthorne event.