I would strongly suggest using a combination of three inexpensive systems to protect yourself from harm and theft.
And, the reason why is that you want to attract as many witnesses as possible to catch a criminal on the spot.
And, even if a criminal does happen to get away with it at a particular time at least your property can still be tracked and traced quickly by both you and/or law enforcement.
- Use the copdots pen to protect your bike and all of its parts: Protect your back pack and bike helmet and bike pump and bike tools and many other related items in case these items are stolen from you out on the streets or when they are inside your home or apartment: COPDOTS Pen Home Asset Marking System - YouTube: http://youtu.be/at2t-ob5WZ0
- There are also GPS tracking systems for your bike http://vectortrac.com/.
- Not to mention, there are personal alarms for walking, running, and biking http://www.dobermanproducts.com/.