Donald Trump. Carlo Allegri/Reuters When President-elect Donald Trump tweets about a public company, the market listens.

And if you hold the stock of one of the companies that has come into Trump's crosshairs, finance app Trigger thinks you'll want to know about it.

The free iPhone app works by letting you set up financial "triggers," which you can then use to guide your investment decisions. For example, you can set a reminder to sell a stock when its price reaches a certain level, moves a specific percentage, hits a one-year low or high, and so on. When the condition occurs, Trigger sends you a notification, and you can decide whether to act on it.

Now the company has rolled out a special "Trump trigger." The trigger "gives you the ability to trade stocks based off of Trump’s tweets about public companies," the startup wrote. Basically, the trigger works by notifying you if Trump tweets about a publicly traded stock that you own, in real time.

Trump has tweeted about companies from Apple to Amazon to AT&T — and that's just the A's. In some cases, such as when Trump blasted Boeing for the cost of a new Air Force One jet, the aerospace company's stock immediately fell nearly 2%.

Should this pattern continue during Trump's presidency, it's not difficult to see why investors might want to be quickly alerted to tweets about their holdings.

Trigger characterized the Trump trigger as the first step toward the startup using "not just price based data but relevant world events to condense into simple IF this, THEN that rules." Expect a bunch of varied types of financial signals in the future.

If the idea of setting up these types of notifications for your investments intrigues you, check out Trigger's website, or its iPhone app.