Mechanical sensors or switches which are best suited for low frequency vibrations and respond to displacement. Piezoelectric sensors are best suited for high frequency vibrations and are sensitive to acceleration. Vibration sensors are sensors measuring, displaying, and analyzing linear velocity, displacement and acceleration. Sensors are normally available with their contacts “normally open” type. In some of the sensors, frequency range and sensitivity are manually adjustable. Vibration sensors or vibration transducers used wirelessly to monitor the system can be used directly mounted on the equipment. The vibration sensor working is based on mechanical, electromagnetic, or optical principles to detect equipment vibrations. The usual range is from 10 mV/g to 100 mV/g depending on the application requirement and the sensitivity of the vibration. Velocity sensors are electrodynamics and do not require external power and the vibration sensor is used for medium frequency measurements.