People have become increasingly aware of the environment in which they live in recent years. This awareness has prompted the development of a reliable environmental monitoring system. This paper presents an energy-efficient and low-power sensor node that could be used for outdoor Internet of Things (IoT) applications to monitor real-time environment conditions such as humidity and temperature remotely. The proposed sensor node could directly connect with a cellular base station over GSM/GPRS quad-bands 850MHz,900MHz,1800MHz, and 1900MHz without needing any Access Point(AP) in the network. The sensor node consists of a central controller based on Atmega328, a communication module on SIM800, DHT22 temperature, and a humidity sensor with a solar-powered charging system. The system is specially designed for robust IoT outdoor applications such as environment monitoring in wilds, large-scale farms, forests, etc. For optimal usage of the power of the battery, an energy-saving mechanism is proposed based on deep sleep scheduling, thus considerably reducing the power consumption and prolonging the up-time of the sensor node.