their respective axes as a result the cord 20 can be moved up and down by pulling on 20 a 20 b thereby activating the mechanism 18 either in one direction or the other however if the cord 20 is no longer tensioned by device 200 it cannot counteract the forces of springs 316 a 316 b therefore the springs pull or push the two gears 312 a 312 b toward each other until their teeth engage and intermesh with the teeth of sides 344 a 344 b respectively as shown in fig1 the central member 344 is fixed and cannot move or rotate once the gears 312 a 312 b come into contact with the teeth of sides 344 a 344 b the gears are immobilized and prevented from rotation by member 344 in this manner the cord 20 is disabled and cannot be used to operate control mechanism 18 in the embodiments discussed above means are provided to lock both sides of the cord by training the cord about the pulleys of gears and selectively immobilizing the gears to prevent each side or portion of the cord from moving in another alternate embodiment a single gear is provided to immobilize the cord only on one.