How many volts are needed to make someone pass out?

The voltage itself is not the primary factor that determines whether someone will pass out from an electric shock; rather, it's the current (measured in amperes) that flows through the body that poses the danger. Typically, a current as low as 100 milliamperes (0.1 amperes) can cause loss of muscle control, and around 200 to 300 milliamperes can lead to cardiac arrest. The voltage required to produce such currents depends on the resistance of the body, which can vary widely, but household voltages (120V or 240V) are often sufficient to cause serious injury or loss of consciousness.