Final answer:
To safely ensure that voltage is turned off before touching electrical terminals, a voltage detector should be used, as it can detect electrical voltage presence without direct contact.
Step-by-step explanation:
To ensure the voltage is turned off before touching any terminals, one should use a voltage detector. A voltage detector is specifically designed to detect the presence of electrical voltage without needing to make direct contact with the electrical conductors. This makes it a safe tool for verifying whether a circuit is live or not before maintenance or inspection work. Alternatives like multimeters, insulation testers, and ammeters have different purposes. A multimeter is a versatile tool that can measure voltage, current, and resistance, but using it alone does not guarantee safety before touching terminals. An ammeter measures the current and is connected in series with a circuit, which requires the circuit to be active and potentially dangerous. Therefore, a voltage detector is the correct answer.