The thermometer market has evolved dramatically over the past decade, with infrared technology becoming increasingly popular alongside traditional contact-based devices. Understanding the science behind each technology helps you choose the right tool for your specific needs—whether that's monitoring a newborn's health, screening employees at a workplace, or simply keeping your family medicine cabinet well-equipped.
This guide breaks down the technology, accuracy, and practical considerations for both infrared and contact thermometers.
How Contact Thermometers Work
Contact thermometers, including oral, underarm, and rectal digital thermometers, measure temperature through direct physical contact with the body. Most modern contact thermometers use one of two technologies:
Thermistor-Based Sensors
The most common technology in digital contact thermometers uses a thermistor—an electrical resistor whose resistance changes predictably with temperature. When the probe tip reaches body temperature, the thermistor's resistance stabilises, and the thermometer calculates the corresponding temperature.
- Advantages: Inexpensive, reliable, well-understood technology
- Limitations: Requires time for the probe to reach body temperature (typically 30-60 seconds)
Thermocouple Sensors
Some higher-end models use thermocouples, which generate a small electrical voltage proportional to temperature difference. These tend to respond faster than thermistors.
Quality contact thermometers typically achieve accuracy within ±0.1°C to ±0.2°C under controlled conditions. This makes them among the most accurate consumer temperature measurement devices available.
How Infrared Thermometers Work
Infrared thermometers measure the thermal radiation (infrared energy) naturally emitted by all objects above absolute zero. This technology allows temperature measurement without physical contact.
The Science Behind Infrared Measurement
Every object emits infrared radiation in proportion to its temperature. Infrared thermometers contain a sensor (typically a thermopile) that detects this radiation and converts it to an electrical signal. The device then calculates the corresponding temperature using known relationships between infrared emission and temperature.
Types of Infrared Thermometers
Forehead (Temporal Artery) Thermometers:
- Measure infrared radiation from the forehead skin surface
- Some models scan across the temporal artery for improved accuracy
- Available in contact and non-contact versions
Ear (Tympanic) Thermometers:
- Measure infrared radiation from the eardrum and surrounding ear canal
- The eardrum shares blood supply with the hypothalamus (body's thermostat), providing readings close to core temperature
- Require proper positioning for accurate readings
Key Takeaway
Infrared thermometers don't measure body temperature directly—they measure surface or tympanic membrane radiation and use algorithms to estimate core body temperature. This indirect measurement introduces potential for environmental factors to affect accuracy.
Accuracy Comparison
Accuracy is perhaps the most critical factor in thermometer selection. Here's how the technologies compare:
Contact Thermometers
- Rectal: ±0.1°C – Gold standard for accuracy
- Oral: ±0.1°C to ±0.3°C when used correctly
- Underarm: ±0.3°C to ±0.5°C – Less accurate due to variable skin contact
Infrared Thermometers
- Ear (Tympanic): ±0.2°C to ±0.3°C – Comparable to oral when used correctly
- Forehead (Contact): ±0.2°C to ±0.4°C
- Forehead (Non-Contact): ±0.3°C to ±0.5°C – Most susceptible to environmental factors
Real-world accuracy can differ from laboratory specifications. Environmental temperature, sweating, recent outdoor exposure, and user technique all affect infrared readings more significantly than contact measurements.
Advantages of Each Technology
Contact Thermometer Advantages
- Higher accuracy potential: Direct measurement minimises environmental interference
- Lower cost: Basic digital thermometers are very affordable
- Proven reliability: Decades of clinical use have refined the technology
- Less affected by environment: Consistent readings in various conditions
- Longer battery life: Simpler electronics draw less power
Infrared Thermometer Advantages
- Speed: Readings in 1-3 seconds versus 30-60 seconds for contact
- Hygiene: Non-contact models eliminate cross-contamination risk
- Non-invasive: Ideal for sleeping children, uncooperative patients, or those with sensory sensitivities
- Convenience: No need to disinfect between uses (non-contact models)
- Multiple uses: Many models can measure surface temperatures for other purposes
Best Use Cases for Each Type
When to Choose Contact Thermometers
- Clinical accuracy is critical: Monitoring newborns, tracking precise temperature changes
- Budget is a concern: Quality contact thermometers are very affordable
- Indoor use only: Environmental factors aren't a concern
- Patient is cooperative: Can hold still for 30-60 seconds
When to Choose Infrared Thermometers
- Screening multiple people: Schools, workplaces, events
- Young children or babies: Quick readings for restless subjects
- Night-time checks: Measure without waking a sleeping child
- Infection control: Reduce contact and cross-contamination
- Convenience priority: When speed matters more than absolute precision
Factors Affecting Infrared Accuracy
Understanding what affects infrared readings helps you get more consistent results:
- Ambient temperature: Extreme room temperatures can affect readings. Most devices work best between 16°C and 35°C.
- Sweating: Evaporative cooling from sweat can lower forehead readings
- Recent outdoor exposure: Wait 15-30 minutes after coming indoors from hot or cold weather
- Hair, hats, headbands: Ensure forehead is clear and clean
- Dirt on sensor: Keep the infrared sensor clean for accurate readings
- Distance: Non-contact thermometers must be held at the correct distance (usually 3-5 cm)
Making the Right Choice
Consider your primary use case when choosing between technologies:
- Family with young children: A combination approach works well—an infrared thermometer for quick screening and a contact thermometer for confirming concerning readings
- Single adults: A quality oral contact thermometer provides excellent accuracy at low cost
- Elderly care: Ear thermometers offer a good balance of accuracy and ease of use
- Workplace screening: Non-contact forehead thermometers are the practical choice
For most Australian families, having both types provides the best of both worlds. Use a non-contact infrared thermometer for quick checks and middle-of-the-night monitoring, and keep a reliable contact thermometer for situations requiring maximum accuracy.
Looking to the Future
Thermometer technology continues to evolve. Emerging innovations include wearable continuous temperature monitors, smartphone-connected devices with tracking apps, and improved algorithms that compensate for environmental factors in infrared readings. As technology advances, the gap between infrared and contact accuracy continues to narrow.
Whatever technology you choose, the most important factor is learning to use your thermometer correctly and consistently. A properly used mid-range thermometer will outperform an expensive one used incorrectly every time.