ESPHome lets a device configured only as a Wi-Fi access point open its controls directly on a connected phone, without internet. Its web interface is embedded in the firmware instead of being loaded from an unreachable website.
Joining the device’s network opens the control page automatically when it uses the standard web port. J. Nick Koston verified live readings, switches and logs on ESP32 and ESP8266 with an iPhone. Devices that normally join a home network and only use an access point as a fallback retain their existing behavior unless the local interface is explicitly enabled.