Mark Zuckerberg and Priscilla Chan at a 2018 event in Mountain View, California.

At work, it’s been a tough run for Facebook CEO Mark Zuckerberg: the company has endured a series of scandals, an exodus of executives, declining and stalling growth and poor stock performance. There have also been calls for Zuckerberg to vacate his role as chairman of the board (which Zuckerberg told CNN doesn’t currently “makes sense”).

At home however, Zuckerberg seems to be carrying on with his role of doting husband and father. Saturday, Zuckerberg shared the “sleep box” he built to help his wife, Priscilla Chan. It’s a wooden box which sits on her bedside table and emits a soft light between the hours of 6 a.m. and 7 a.m., according to Zuckerberg.

“Being a mom is hard, and since we’ve had kids Priscilla has had a hard time sleeping through the night. She’ll wake up and check the time on her phone to see if the kids might wake up soon, but then knowing the time stresses her out and she can’t fall back asleep,” Zuckerberg wrote on Facebook.

Zuckerberg and Chan have two children: Maxima, 3, and August, almost 1.

The light from the “sleep box” lets Chan know whether it’s time for her or Zuckerberg to get up without her having to know what time it is specifically.

The light is “visible enough that if she sees it she’ll know it’s an okay time for one of us to get the kids, but faint enough that the light won’t wake her up if she’s still sleeping. And since it doesn’t show the time, if she wakes up in the middle of the night, she knows to just go back to sleep without having to worry about what time it is.

“So far this has worked better than I expected and she can now sleep through the night,” Zuckerberg said.

Thrive Global founder Arianna Huffington, who is an advocate for the importance of sleep, responded to Zuckerberg’s post: “Love this! It’s great that you made this device so Priscilla could avoid looking at her phone,” Huffington wrote. (She also took the opportunity to recommend a Thrive Global product, a charging station that discourages you from looking at your phone.)

Zuckerberg said the device was an expression of his love for his wife. But perhaps also a viable business idea.

“As an engineer, building a device to help my partner sleep better is one of the best ways I can think of to express my love and gratitude,” Zuckerberg writes. But “a bunch of my friends have told me they’d want something like this, so I’m putting this out there in case another entrepreneur wants to run with this and build sleep boxes for more people!”