Explanation:

- Option 1: Galvanometer

- A galvanometer is an instrument used to detect small electric currents by deflecting a needle in response to current flow through a coil.

- It is the correct instrument for detecting the presence of a current in a circuit.

- Option 2: Sphygmomanometer

- This instrument measures blood pressure, not electrical current. Used in medical diagnostics.

- Option 3: Barometer

- Used to measure atmospheric pressure. It is widely used in meteorology but irrelevant for electric current detection.

- Option 4: Magnetometer

- Measures magnetic fields and is not specifically used for detecting current, though it can imply current presence when used indirectly.