Purpose: The purpose of this study is to verify factors affecting the use of real-time telemetry system based on extensive ELM in emergency medical service. Methods: During the study, a total of 72,907 patients were transported to a hospital in the city of Wonju via ambulance. For testing Glasgow Coma Scale (GCS) recorded in hospital phase, we merged data which accords with run and medical records mutually, and then extracted 1,406 data. Based on extensive ELM including 3 way-interaction term with contingency factors (a limited situation. e.g. time and distance), we extracted variables from the run and medical records like the qualifications of the EMT, the level of the patients` consciousness (A?V?P?U, GCS), and transport time and distance. Results: The results indicated that EMTs whose the level of expertise is high were more likely to use the RTS when patient`s GCS point is low (GCS 3-8 points) in limited situations such as short transport time or distance to hospital. Also, like the result of previous study, the higher the EMT level, the more A?V?P?U affected the use of RTS, and contrary to it, EMTs with the high level more interacted with the peripheral cue than EMTs of the low level. As assuming that contingency factors result in this opposite result, we tested 3way-interaction term: the level of the patients`consciousness (A?V?P?U, GCS) × the level of EMT × contingency factors (time, distance), respectively. Conclusion: EMTs with higher levels of expertise were more likely to use the RTS when the lower the level of patient consciousness (Pain, Unresponsiveness) was low in limited situations. The contingency factors (time to hospital, distance to hospital) which represent limited situation at scene are important factors to make EMT level 1 choose RTS at scene, although time and distance factors are more in peripheral cue, compared to central cue like A`V`P`U, GCS in medical view.