Put a bloody string on it mate.
You are not alone as there are reports that on the same day one of our JWOC team also lost their SIAC stick in a qualifying race.
At least you can't blame the hardware / software when you lose your SI Stick!
Rather than using string to hold it to your wrist (like the rest of us) you could always get Aoife to follow you around courses and help quickly find it when it goes missing.