Abstract: A signalling device for weight lifters performing exercises involving bending of the knees. The signalling device is provided with mercury switch for sensing deviation of the axis of the portion of the leg to which the device is attached and a buzzer or other signalling device which signals the lifter when that portion of the leg has deviated from the vertical by a preselected amount. The amount of deviation from the vertical required to activate the signalling device may be varied by an optional angle adjustment. The signalling device allows a weight lifter to exercise properly, but effectively, without risking injury.