Mark Zuckerberg will forever be associated with Facebook and social networks, but we can’t forget he’s also an engineer and he just put his talent to good use helping his wife get a good night’s sleep, reports Entrepreneur.

Posting on Instagram, Zuckerberg explained how he spent some time recently building a light-emitting wooden box. It sounds strange until you hear why he created such an unusual object.

His wife Priscilla knows that their children usually wake up between 6-7am, so she got into the habit during the night of checking her phone to see what time it is and whether she needed to get up. The problem is, knowing the time “stresses her out and she can’t fall back asleep.”

The solution, as Zuckerberg viewed it, was to create a new device that indicates when it’s the right time to get up for the kids, but isn’t a distraction at any other time. The end result is a “sleep box.” It’s a very simple wooden box that emits a faint light focused downwards, but only turns the light on between 6-7am each morning. If Priscilla wakes up and the light isn’t on, she knows to go right back to sleep, where as the light being on won’t wake her, but if she wakes and sees it she knows it’s time to get up.