Last year, Ember Technologies, Inc. ran a crowdfunding campaign on Indiegogo to build a mug that keeps hot drinks at the perfect sipping temperature. By now, it’s sold 4,000 of these devices.

And in something of a coup for the startup, Starbucks Corp. has begun selling Ember Temperature Control Mugs in its stores across most of the U.S. and online for $149.95.

Whether it’s coffee, cocoa or tea, hot drinks are usually prepared and served around 160° Fahrenheit, said Ember CEO Clay Alexander — and that’s how cafes and restaurants mostly serve them. Yet, people like to drink hot beverages closer to 130°.

Commonly available thermoses work with simple insulation, but they heat unevenly and don’t cool drinks when they are searing, resulting in plenty of burnt tongues. Ember works with semiconductors inside to bring a drink to the ideal temp and hold it there it for hours, Alexander said.

Out of the box, the Ember mug needs to be charged one time. It is then ready to use. There is an optional mobile app that works in conjunction with the mug. A dial on the bottom allows users to set their preferred temperature on the mug. There are no buttons or moving parts otherwise.

To get their products sold at Starbucks was no easy feat, Alexander said. The coffee giants have a rigorous product evaluation and testing process, encompassing safety, quality and coffee tasting tests, and audits of startups that want to work with Starbucks.

Alexander told TechCrunch that the deal only happened with the help of his board of directors and investors. Working with the design consultancy Ammunition didn’t hurt, either.

Ember has raised funding from celebrity investors, including Demi Lovato, Nick and Joe Jonas and the DJ Kascade, among others.

Additional temperature-control products are in development using Ember’s patented systems. The startup wants people to be able to warm or cool liquids of every kind, without requiring any ice or open flames. So stay tuned for temp-controlled baby bottles, serving dishes and more, Alexander said.