Thermistor temperature probes sense temperature by using thermistors, devices made of semiconductor materials which exhibit a large change in resistance for a small change in temperature. There are many different probe configurations. Most suppliers specify a thermistor temperature probe by application or intended use. Custom products are also available. Air probes are thermistor temperature probes for air-flow temperature measurements. Angled probes can be used inside pipes or angled spaces. Clamp probes or strap sensor probes clamp or wrap around the surface to be monitored. Curved probes are used to measure temperatures on pipes or other curved surfaces. Drop probes are designed for well or underwater applications. Flat probes or ribbon probes have a flexible membrane. Flexible probes can be manipulated for various temperature measurements. Penetration probes or needle probes are used to measure internal temperatures. Roller probes or moving probes are used to measure temperatures on moving surfaces. Straight probes can be used in wells and designed to measure stationary surface temperatures.