Car makers have made great improvements in preventing car thefts. My car key has an electronic tag embedded within it. The car is not suppose to start unless it can talk to that tag so the key has to at least be in the car. This makes the the car extremely difficult to hot wire. But there is an unintended consequence to this advancement in security — car thieves are starting to break into people's homes to steal the car keys.

I have been reading a history book focused on the sixteenth and seventeenth centuries. It had an example of a similar unintended consequence to a security measure. With the use of canons, castle and city walls did not provide as much protection during sieges as they formerly did. An architectural response was to build large earthen bulwarks around the walls to absorb the shot and add bastions to provide better offensive positions for the defenders. The manning of the bastions required many more soldiers to be resident in the cities. This changed the strategy of advancing armies. Previously, they might have passed by a well-fortified city since it did not present a threat to the army. Now they tended to set siege to these cities. Otherwise, they were leaving a large military force behind them that could attack their vulnerable rear.