Draper screwdriver type testers contain an indicator in the handle which lights up when the point is touched on voltages between 220-250V and a finger or thumb is placed on the end of the tester to create a circuit. Non-contact voltage detectors work by sensing the fluctuations in the electric field which surround AC charged objects. This means no contact with the circuit is ever needed giving the user extra safety.
140MM Mains Tester
