Bruce Schneier writes a very interesting blog on security issues. His focus is most often computer security, but he also covers physical security.
He talks a lot about the difference between feeling secure and being secure. He introduced me to the term "security theater", where the security measures are very visible, but not very secure. He also talks about using security as an excuse to reduce privacy.
His latest entry is one of those--A recent government regulation requires Tire Pressure Monitoring Systems on all new vehicles. These are sensors in the wheels that measure and broadcast a short-range signal intended to let the driver know if his pressure is OK. However, there is nothing that keeps the signal from being picked up outside the vehicle--That means it would be relatively simple to see when any vehicle equipped with these sensors has passed a particular point. Existing highway speed sensors could be modified for this.
If you are at all interested in privacy and security, he's almost always a good read.