The body temperature measured by the skin is easily affected by the measurement environment such as temperature or humidity, and in some cases, the difference from the central body temperature is particularly large. Therefore, there has been an attempt to develop a new method of measuring skin body temperature to predict the central body temperature by measuring body temperature in the skin. The purpose of this study is to evaluate the effectiveness and safety of the core temperature measured using this medical device by comparing the accuracy of the body temperature measured through the XST600 electronic thermometer applying the HF technology developed by Chois Technology with the body temperature measured by the Gold Standard 3M Bair Hugger Temperature Monitoring System Model 370. - Number of target subjects: 117 in total - Basis for calculation: This clinical trial is an corroborating clinical trial to confirm the clinical accuracy and effectiveness of the test equipment (XST600), so it is set based on the requirements of ISO 80601-2-56 (the "Medical Device Standard" 50. Electronic thermometer). 1. Total number of target subjects: 117 (105 + 10%) * At least 105 participants are required in accordance with ISO 80601-2-56:2017, and 117 participants are targeted by applying the normal research dropout rate of 10%. * If the research procedure is completed in 105 participants without dropping out, the study is terminated. ① Normal body temperature subject: 82 (73 participants + 10%): Those with a core temperature of 36.1℃ (10) or more and 38.0℃ or less when measured by RCT. * If the research procedure is completed in 73 participants without dropping out, the study is terminated. ② Number of subjects with heating: 35 (32 participants + 10%): Subjects with a core temperature of 38.0℃ or higher when measured by RCT * According to ISO 80601-2-56, the maximum number of subjects with heating is 32, by applying the standard that should not exceed 30%, and the target is 35, by applying the normal research dropout rate of 10%. * If the research procedure is completed without dropping out of only 32 subjects, the study is terminated.

This study is designed to simultaneously apply both the test and control devices to each subject. All subjects (N = 105) will have the sensors attached at the same anatomical position; therefore, no group assignment (randomization) will be conducted.

• Simultaneous Measurement: Both the Bair Hugger™ Model 370 and XST600 will measure temperature concurrently.
• Target Core Temperature: Only subjects with a core temperature of 36.1 or higher (as measured by Reference Clinical Thermometer) will be included.

Inclusion Criteria

1. Males and females aged 19 to 80 years.
2. Patients requiring continuous temperature monitoring in the Operating Room or Intensive Care Unit.
3. Subjects (or their legal representatives) who have been fully informed about the study and have voluntarily provided written informed consent.

Exclusion Criteria

1. Skin Conditions: Presence or high risk of skin diseases, wounds, infections, or allergic reactions (e.g., rash) at the application site (forehead).

2. Medication Interference: * Current use of drugs that may interfere with clinical trial results, such as barbiturates (sedatives/hypnotics), thyroid preparations, or antipsychotic drugs (per ISO 80601-2-56).

   o Administration of antipyretics within the last 120 minutes or immunization within the last month (per ISO 80601-2-56).

3. Medical History: Any underlying medical condition that may significantly impact the interpretation of the clinical results.

4. Investigator Discretion: Any individual deemed inappropriate for participation by the principal investigator.

Measurement Methods & Data Acquisition

1. Bair Hugger™ Temperature Monitoring System Model 370

   • Setup: Connect the sensor to the cable connector, ensuring the tab is fully inserted and aligned.
   • Stabilization: Allow a minimum of 5 minutes for the temperature to stabilize.
   • Recording: Once stable, press 'Start' in the app. Data will be recorded for a minimum of 25 minutes post-stabilization.
   • Frequency: Measurements will be recorded at 1-minute intervals.

2. XST600 Measurement Method

   • Recording: Once the measured temperature stabilizes (minimum 5 minutes), press the 'Start' button in the app.
   • Duration: The recording duration shall be at least 25 minutes following the stabilization period.
   • Automation: Upon clicking 'Start', data is automatically saved at 1-second intervals. The process concludes when the 'End' button is clicked.

Inclusion Criteria:

1. Males and females aged 19 to 80 years.
2. Patients requiring continuous temperature monitoring in the Operating Room or Intensive Care Unit.
3. Subjects (or their legal representatives) who have been fully informed about the study and have voluntarily provided written informed consent.

Exclusion Criteria:

1. Skin Conditions: Presence or high risk of skin diseases, wounds, infections, or allergic reactions (e.g., rash) at the application site (forehead).

2. Medication Interference: * Current use of drugs that may interfere with clinical trial results, such as barbiturates (sedatives/hypnotics), thyroid preparations, or antipsychotic drugs (per ISO 80601-2-56).

   o Administration of antipyretics within the last 120 minutes or immunization within the last month (per ISO 80601-2-56).

3. Medical History: Any underlying medical condition that may significantly impact the interpretation of the clinical results.

4. Investigator Discretion: Any individual deemed inappropriate for participation by the principal investigator.

Age and Gender: Men and women aged between 19 and 80 years. Clinical Requirement: Patients who need to monitor their body temperature in the operating room or intensive care unit at Severance Hospital. Voluntary Consent: Subjects (or their legal representatives) who have received a detailed explanation of the study and have voluntarily provided written informed consent. Baseline Temperature: Only subjects with a confirmed core temperature of 36.1 or higher (as measured by a Reference Clinical Thermometer) will be included.