Consistent exposure of hazardous, harmful or toxic gases has become a major issue in worldwide due to more stringent environmental or safety regulations. With a view to tailor the sensor properties, an attempt has been made to incorporate the copper (Cu) and silver (Ag) metal ions into NiO films through DC reactive magnetron sputtering technique. This book is mainly focused on the optimization of the structural, compositional, micro-structural, optical and electrical properties for gas sensor studies. Finally, systematic film deposition and annealing conditions have been carried out and attained the enhanced gas sensitivity at low temperatures.