rotate the shaft as the knob 60 is rotated in a clockwise direction the floating plate travels upwardly first extending spring 50 spring 51 is not initially extended with wire 56 on the end thereof sliding through a hole in the floating plate as the plate rises the tension on the lever arm increases and the force exerted by foot 48 on the tube 8 at the other end of the lever arm also increases as the floating plate continues to rise heavy spring 51 is also extended thereby increasing the force of the lever arm on tube 8 very substantially accordingly by tightening or loosening the pair of tension springs 50 and 51 the force of the tug exerted by a fish on the line necessary to trigger microswitch 40 can be varied along an extremely wide range of sensitivity the electrical circuitry embodied in the apparatus of the invention also includes means to alert the fisherman when the microswitch is tripped a light 66 is visually perceptible and a buzzer 70 is also actuated the alert mechanisms are operated by a microswitch 67 mounted on plate 31 which has a short downwardly extending lever arm 68 when the solenoid is actuated and the catch released the catch moves from the position shown in fig2 to the position shown in fig3 with the upper edge of catch 21 contacting lever arm 68 of the microswitch actuating the switch and the alert means a very important feature of the invention is the mechanism for calibrating the sensitivity of the device after it is cocked a toggle switch 65 at the top of the apparatus is movable between an 34 operate 34 position and a 34 calibrate 34 position when the switch is.