Can Chuango Wi-Fi Alarm OV-300 be used without a power supply?

No. The Hub does not have built-in battery. But you could lift up the battery cover at the bottom of Chuango WiFi Alarm OV-300 and insert provided four AA batteries. Even when the power goes off, your Chuango WiFi Alarm OV-300 could still work for about 24 hours and keep your home under protection.