Attachable sensor for putting stroke path and plane detection

A putter trainer device for detecting inaccuracies in a golf putting stroke is disclosed. The putting trainer device is releasably attached by a clip (2) to a shaft of a golf putter and includes two guided ramps (19A, 19B) with each ramp having an active position and a neutral position. In one embodiment, a free rolling disc magnet (20A, 20B) is located upon each guided ramp and each free rolling disc magnet is biased towards the neutral position (23A, 23B) on its respective ramp. The movement of either free rolling magnet from the neutral position to the active position is detected by magnetic reed switches (25A, 25B) located adjacent to each ramp. A speaker is activated when the magnetic reed switches detect that either free rolling magnet has moved from the neutral position to the active position.