To tap into a wire, it's good to cut it, bare a little wire on each end of the cut & tin each of the two ends. Then tin the end of the additional wire you wish to use. You can then slip on 4 - 5 cm of heatshrink, say ~5mm diameter would be good in this situation. Then secure the three tinned wires together, so that approximately the orginal length is retained, and solder away - keep the heatshrink far away down the end of the purple wire - once the joint is cool, you can slip the heatshrink back down - heat with a hairdryer up close or wave a lighter under it brifely - if you put it on the right side of the joint, then everything will be covered up very neatly & professionally. I've been reviewing & making a small changes here and there to the double click circuit, and here's the latest version. It's got a couple of filter's whacked in to keep the QT113 happy/noise free. The QT113 only needs 2.5v!, the 555's only need 4.5v and voltage drop through the filters should be very minimal. It seems all the QT113's here are active low. I'm thinking of getting an smd version to keep costs low cos i'll be getting 10 of them - a couple of separate pcs & a couple of spares.