springs 340 to ride over and lift the ends 342 of the triangular catch members 336 338 this rotation of the triangular catch members 336 338 rotates the tilting block 330 and disengages the threaded portion 328 of the tilting block 330 from the screw shaft 326 when the tilting block 326 is disengaged from the screw shaft 326 springs 340 drive the tilting block 330 and the block 342 to the right thereby retracting the key 302 into the housing during the slight pressing of the button 304 the catch 332 continues to lock the gear wheel 320 the block 342 does not have any threads and is thus free to slide pressing the button 304 fully causes the catch 332 to release the gear wheel 320 as described above a conventional escapement mechanism may be used to control the pressing of the button and alternates a full pressing and a slight pressing action as shown in fig1 a spring 350 mounted on the block 342 presses against the tilting block 330 into engagement with the screw shaft as shown in fig1 the catch members 336 338 slide within guide walls 352 354 formed in the housing 12 and which are shaped to control the orientation of the catch members 336 338 as is shown in fig1 the embodiment of the invention 10 may be powered by a clock spring 332 as shown schematically in fig9 alternatively the embodiment of the invention 10 may be powered by a clockwork mechanism 360 as shown in fig1 and 19 forming a third embodiment 300 of the invention the clockwork mechanism 360 incorporates a clock spring 362 a.