GPS tracker?
 

Has anyone seen or used something like this. Seems this stuff used to be big $ but are getting cheaper.

Seems like a good security option. Can even alert you if your bike moves. And it tells you right where you bike is.

Mini GPS GSM GPRS Vehicle Car Spy Realtime Tracker Tracking System Device TK102 | eBay

Security or a few teenage kids... I see multiple uses!

Yeah, teenagers, elderly, young kids, dogs, wives. Lots of uses. I think you only need a sim card but no monthly cost(?)