Thermometers for twins

One good thermometer covers two babies. Fevers do not schedule themselves simultaneously (usually), and even when both twins are sick, one accurate device beats two mediocre ones. For infants, accuracy is the whole spec: pediatricians still want rectal readings for young babies, so make sure your setup covers that, whatever else it does.

Buy new. Thermometers are cheap, hygiene-adjacent, and calibration is not something you can verify on a used device. The twin-specific tip is bookkeeping, not hardware: when both babies are sick, you will not remember whose 38.2 that was. Log readings by name, and keep the thermometer where the 2am parent can find it without lights.