Which of the following might damage a multimeter?

The correct answer focuses on the potential damage that can occur when a multimeter is incorrectly set. When measuring voltage while the multimeter is set to measure resistance, the device may apply a small test voltage to the circuit. If there is a substantial voltage present in the circuit being tested, this can exceed the multimeter's limits, potentially damaging the internal components.

The other scenarios presented, while they may not be advisable practices, are less likely to induce permanent damage. Measuring a voltage that is too small generally does not harm the device; it simply results in an inaccurate reading. Leaving the meter in the milliamps position overnight is an improper usage that could drain the battery, but wouldn't damage the multimeter itself. Not allowing it to warm up might affect measurement accuracy in precise applications, but it does not lead to physical damage of the device. Understanding proper usage and settings of a multimeter is crucial in maintaining its integrity and functionality.