If you've got an old Android phone, have wifi and a power socket near your bikes this free security app looks fantastic.

http://www.salient-eye.com/

For nowt, it looks like a cracking app. Just need perform surgery on an old stuffed toy to hide the phone. (Just read the FAQs - Don't.)

Similar thing reported here for iDevices

http://www.bbc.co.uk/news/business-31157992

Amazing how all the tech in a smartphone packaged together and easy to fiddle with, yet they are worth less than the component parts