These replacement probe covers are only suitable for use with the Omron Gentle Temp 520 and the Gentle Temp 521. They are not compatible with any other Omron thermometers. For hygiene reasons we recommend that a probe cover is used every time the thermometer is used. Fever is one of the most important vital body signs. Monitoring fever in an early stage will allow for quick and active response. Omron pays the highest attention to the development of functional and accurate fever monitoring tools. With an user-friendly ergonomic design for extra comfort, the Gentle Temp 521 ear thermometer is especially suitable for use with youngsters. In addition to the convenience of the backlight display it uses infrared technology to provide results in just one second so that highly accurate measurements can be taken with the minimum fuss. Giving users extra flexibility, the Gentle Temp 521 ear thermometer offers ﾑ3 in 1ﾒ temperature measurement. It not only measures ear temperature but can be used to take surface temperatures, from a milk bottle or food dispenser for example, as well as giving readings for the room temperature. The Gentle Temp 520 ear thermometer uses the same highly accurate technology as the 521 and includes some of its features, including one second measurement and a memory for up to nine readings to track temperature over a period of time and monitor trends. It comes complete with 21 probe covers. Temperatures can be displayed on the large LCD screen in either Degrees or Fahrenheit. Pack of 40 probe covers for use with the following OMRON GentleTemp thermometers: GentleTemp 520 GentleTemp 521 GentleTemp 522 Pro