An electronic thermometer includes a probe adapted to be heated by a subject for use in measuring a temperature of the subject. At least one temperature sensor detects a temperature of the probe. A probe sensor detects a condition at the probe. The probe sensor has an idle condition when the probe is not inserted into the subject. A processor is operatively connected to the probe sensor and programmed to monitor a change in the condition of the probe sensor from the idle condition to determine whether the probe has been received in a probe cover and inserted into the subject.