(CNN) Mark Zuckerberg and his wife, Priscilla Chan, are experiencing the joys of parenting -- including sleep deprivation.

"Being a mom is hard, and since we've had kids Priscilla has had a hard time sleeping through the night," the Facebook founder and CEO wrote Sunday in an Instagram post. The couple have two young girls.

"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."

To help Chan get more shuteye, Zuckerberg used his engineering knowledge to devise a "sleep box."

No, she doesn't sleep inside the box. Placed on Chan's nightstand, the device emits a "very faint light" between the hours of 6 to 7 a.m. to let her know if it's time to get up. If it's not lit, Chan will know it's OK to fall back asleep. This way, she won't have to check the time, which can be a stressor.

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