Do these monitors require Wi-Fi, and what happens if it goes out?

Yes — both Nanit and Owlet rely on Wi-Fi for full functionality. Verified-purchase reviewers and r/beyondthebump threads cite intermittent connection issues as the most common frustration. Some Reddit commenters in r/predaddit note Nanit can work on a local network, but for streaming away from home and for app alerts you need a stable connection. Parents specifically wanting a non-Wi-Fi monitor consistently steer toward dedicated parent-unit systems instead.