Hi Matthew!
I've had remarkably good luck with an offering made in China and offered on eBay. Fellow Forum member Andre Jute also bought one and at last count, seems happy with it for what it is/does -- a small noisemaker that makes life a tiny bit more difficult/distracting for a would-be thief. Biggest benefit for me is hearing if someone is bothering the bike or panniers when it is locked and near but just out of sight (i.e. just outside a restroom, or outside my tent).
To read more about it, go here:
http://www.thorncycles.co.uk/forums/index.php?topic=3896.msg17158#msg17158And to see pictures of it mounted, go here:
http://www.thorncycles.co.uk/forums/index.php?topic=3896.msg17095#msg17095http://www.thorncycles.co.uk/forums/index.php?action=dlattach;topic=3896.0;attach=1034In truth, the failure rate was about 40% dead-on-arrival, but the eBay seller made good and the price was remarkably low...as I recall, my last one was under USD$4.25 postpaid, so it was okay. If they fail, they seem to do so as the result of a short and simply stop working or the alarm becomes an almost inaudible squeak. If they work to start, they keep on working.
I hope this helps; good to hear from you! If you decide to get this alarm or another, please let us know how it works for you so we can add it to the list of possible solutions.
Best,
Dan.