Safety 1st 3-in-1 Nursery Thermometer is designed to measure the body temperature of a baby easily. It can be used to check the baby's temperature in 3 ways – oral, rectal, and under-arm. The thermometer displays the reading within 30 seconds. It beeps when the reading is ready. The over-insertion gauge is helpful while taking the temperature rectally as it ensures that you do not insert it too much inside.