IC temperature sensors contain not only a temperature sensor but also signal-conditioning circuits. These sensors will produce a voltage or current output that is linearly proportional to temperature. Some even digitize the temperature and produce serial outputs. Most of these devices are packaged in standard IC packages for mounting on circuit boards and they all require a DC voltage source, typically 2.7 V to 5 V. IC temperature sensors may require you to design your own electronics to digitize the analog output or to interpret the digital serial output. Sensor manufacturers provide application notes with sample schematics to help you with your design.
Infrared thermometers measure the surface temperature of objects within their field of view.
The size of the field is important if you're trying to measure the temperature of a single object. The field of view is inversely proportional to the distance to the object. Check the manufacturer's data sheet for this specification. You can use a variety of instruments to measure temperature with probes. Simple meters may not store any measurements while others store from several readings to more than 100,000 readings.