Temperature sensors are measurement devices that determine temperature by sensing some physical characteristic, such as electrical resistance, electromagnetic field (EMF), or thermal radiation. There are many different types of products. Examples include thermocouples, resistance temperature detectors (RTDs), thermistors and bimetal switches, temperature sensor kits, and temperature and liquid level sensor combination units. Temperature measurement range, accuracy and stability are the most important specifications to consider when selecting temperature sensors. Additional parameters include probe type, tip and termination style, and electrical output. Products with visual displays and audible alarms are commonly available.