How many of you call home every time just before arriving there? And why not?
I can give you a damned good reason why you should without fail - safety, yours and your loved ones.
Duress codes are something that every family should have and use. Here's just one example of why: You own firearms and somebody spots you leaving your house with one on the way to the range, militia gathering, hunting, whatever and marks your house. They come back and break in only to find that your guns are locked in a safe. Meanwhile, your wife comes home and becomes an instant bargaining chip - they'll hold her waiting for you to come home and say they will kill her if you don't give up the combination to your safe when you come home.
But wait! You call and the thieves let her answer the phone (she insists she has to answer it or you'll suspect something's wrong) and you ask a simple, common prearranged question. She gives the prearranged answer in a normal conversational tone and you instantly know all is not well on the homefront allowing you to either call 911 or take care of business yourself.
For the Patriot, it works both ways as well - the house has been raided, the cops are waiting for you and now you've been alerted and can move out smartly to a location known only by you and her. This protects her as well - she can't be prosecuted for warning you.
Think about it - yeah, it's a pain in the ass sometimes but it only takes one time for it to pay off.