Rectal digital thermometers are most accurate, especially for babies under 3 months. For older babies, ear and forehead thermometers are accurate enough for home use. Accuracy difference is typically 0.1-0.3°C.

Infrared forehead thermometers can be used from 3 months onwards for screening. For newborns under 3 months, pediatricians recommend rectal temperature as the gold standard because fever at this age can be a medical emergency requiring accurate measurement.

Infrared readings can vary due to: sweat on forehead, hair covering forehead, just came from hot/cold environment, dirty sensor lens, low batteries. Take reading 20-30 minutes after bath/feeding, wipe forehead dry, and take 2-3 readings to average.

Rectal: 38°C (100.4°F) or higher is fever. Oral: 37.8°C (100°F). Underarm: 37.2°C (99°F). Forehead readings are usually 0.3-0.5°C lower than rectal. When in doubt, confirm with rectal for babies under 3 months.

Digital thermometers can last 3-5 years with proper care. Replace batteries annually even if working - weak batteries affect accuracy. Replace immediately if display is faded, readings seem wrong, or probe tip is damaged.

For families with newborns: buy both a digital (for accurate rectal readings) and infrared (for quick checks). For babies 6+ months: a quality infrared forehead thermometer handles most needs. Keep a basic digital as backup.

For digital thermometers, ₹200-400 options are excellent. For infrared, spending ₹1,000-1,500 gets you better accuracy and features. Premium ₹2,500+ models are worth it for medical-grade accuracy or multi-function convenience.

Babies under 6 months have very narrow ear canals. The ear thermometer probe doesn't fit properly, leading to inaccurate readings. The probe may also miss the eardrum and measure canal wall temperature instead.