The present paper relates to a development of the Gear Detection Sensor, and more particularly, to a rotary position sensor to detect gear shifting by rotation of control lever in automatic transmission, which includes a sensor module based on half ring shaped permanent magnet and linear Hall IC as electromagnetic elements for non-contact measuring for gear detection. After conducting actual experimentation using exclusive tester and magneto-static FEM analysis, it is described to consider possibility for automotive application at automatic transmission based on the result of total error analysis.