Fires are serious risks that can occur in any home, especially when appliances are not used or maintained properly. Traditional fire progress in a room can be divided into four main stages: incipient, growth, fully developed, and decay. Early detection of a fire at the initial stage makes it easier to extinguish the fire and minimize damage. Smoke detectors and vision-based fire detection methods can only recognize a fire accident when it enters the growth phase. Infrared thermal sensors can detect the temperature increase of objects early in the fire development progress. This paper presents the use of a low cost, off-the-shelf far infrared thermal sensor to build an indoor fire early warning system. The proposed system takes the advantage of the LoRa transmission technology and the internet-of-things (IoT) technology to perform real-time fire detection, monitoring and warning. The designed thermal sensors successfully detected the temperature change of the object and the presence of fire in the monitored area. The system’s web application allows the authorities to observe thermal images of monitored rooms in real time, sending warnings when a fire incident occurs. The proposed method can provide a potential solution to improve the effectiveness of early fire detection for urban areas.