This paper presents the research results of building a monitoring system and real-time early warning using the GNSS-RTK technique. The object of the study is to establish and operate a real-time warning program using a light with input data from GNSS-RTK observations that filtered outliers following a normal distribution. The study uses a base, a rover, the single base method at 17 km, 10 Hz sensitivity, and 1 Hz sample interval. The method of corrections transmission is the 4G network, and the NTRIP protocol. The early warning program is coded by C# language combined with an ESP8266 wifi module. The result of the study is successfully building a warning system using an alert light and operating smoothly. These are also the initial results to expand warning mode with phone messages or email and build a complete warning system for many rovers in different locations.