What is the reason that WiFi monitors offline

Check the distance of indoor monitor to the router, please make sure indoor monitor has WiFi signal

If the distance is long and it is not easy for you to place the indoor monitor closer to router, you can buy a repeater

If the indoor monitor is with wired function, you can just use wired mode to connect indoor montior and router, that will be more stable,

Make sure do not connect many devices (mobile phone, pad, pc) to one router.