Abstract: A device for monitoring the exercising of body muscles or the like. The device has a body that is provided with a passageway from one side to the other through which can be passed any conventional belt-like member. Positioned within this passageway is a switch operator that is mounted so as to deform when increased tension is applied to the belt-like member. Upon adequate deformation, this operator causes a first switch contact to engage a second switch contact to complete a series electrical circuit containing both an audible and visual signal-generating unit. The spacing between the first and second switch contacts is adjustable by a user at any time, even while in use, to thus adjust the sensitivity of the device. The adjustment feature also provides an "on/off" switch for the device.