A deep tendon reflex-eliciting device actuated by pressure against a patient's skin, which releases a spring-loaded mass that delivers an impulse through a fully-enclosed housing. This device includes a weight contained within the casings, and a mainspring in communication with the weight. The mainspring has a bias toward expansion. In the compressed position, the mainspring is also compressed, and the weight is pushed backwards into the rear casing. The weight is released to be driven forward by the mainspring. The weight strikes the inside of the forward casing, delivering an impulse to a surface against which the device is pressed. A reset spring can push apart the forward and rear casings to reset the device to its expanded position. A case screw is also included which is able to consistently set the impact force of the device.