Add a little extra weight to your water bottle cage. Bike alarm.

[Paul Nevins]

Will work until thieves learn how to disable it. Maybe a device slipped into the handle bar, or onthe BB powered by the crank.

http://1sun4all.com/bikes/bikespike-new-device-lets-you-track-your-bike-and-detects-thefts-crashes/

[Margareth Demery]

Yes, it does not look very secure and I certainly don't want to give up my extra bottle cage. A bit pricy at $199.  I never let my bike out of my sight....