Laboratory thermometers are used to measure temperatures or temperature changes with a high degree of precision. They are made of metal or glass and strengthened through processes such as thermal tempering or annealing. Several types of laboratory thermometers are commonly available. Liquid-in-glass thermometers are made of sealed glass and contain a fluid, usually mercury or red alcohol, whose volume changes relative to its temperature. Bimetallic strip thermometers include two different metals that are bonded together and expand at different rates as they warm up. Often, long bimetallic strips are wound into a coil and used with a dial. Electronic devices such as thermistors measure changes in electrical resistance and convert them to changes in temperature. Infrared thermometers are non-contact devices that convert infrared (IR) energy to an electrical signal that can be displayed in units of temperature. Other specialized or proprietary products are also available.