The Old "Credit Card Trick" Explained

I’ve seen countless movies where a spy or villain covertly enters a building by slipping a credit card between the door and the frame, gaining access instantly.  In reality however, most lock manufacturers produce latching devices known as deadlatches that are sold with all of their keyed doorknobs and levers.  Deadlatches feature a spring-loaded latch bolt and a plunger.  When the door is closed, the latch bolt enters the strike plate and secures the door.  The deadlocking plunger however, is pushed into latch assembly.  This plunger immobilizes the latch bolt unless a knob, cam or lever handle is engaged.  This prevents what is called “jimmying” or “loiding”.

So the credit card trick is only a thing of the movies?

Not quite.  Deadlatches for cross-bored locksets have a plunger that is very small and can become lodged in the same hole as the latch bolt if the strike or frame are not in proper alignment.  When the deadlocking plunger projects, the latch bolt is free to be pushed back.  Also, doorframes can shift over time, either from humidity, routine wear, temperature or the building settling.  This can sometimes result in a lockset that can be loided or it could also lead to a door that will not latch shut. 

Schlage F-Series deadlatch, not installed.  This is what you would find on the shelves at most hardware stores.  Note the deadlocking pin on the left

Now a strike plate has been placed in front of the latch to simulate a closed door.  The plunger is pressed in by the strike.  The latch cannot be pushed back now

In this photo, the plunger has entered the hole in the strike.  This latch could now be loided with a credit card, screwdriver or other tool

Fortunately, there is a solution:  If you’re a homeowner, the most practical and affordable remedy to this problem would be to install a deadbolt in addition to the keyed knob or lever that is already on the door.  Most deadbolts also have a 1” throw, compared to the 5/8” throw of most deadlatches.  The longer bolt throw makes it difficult for burglars to create a large enough gap between the door and the frame to force the door open.

However, if you own or lease commercial establishment, you will be very limited in your use of deadbolts by fire and building codes.  Some code-compliant alternatives could include selecting mortise locks instead of cylindrical locksets at the time the structure is built (mortise locks typically have a deadlocking plunger that is further from the latch bolt).  Also, various manufacturers make protective plates that shield the latch to frustrate loiding attempts.  Check the fire and building codes in your area before making any modifications to the security hardware at your site.

Most burglars tend to follow the path of least resistance and gravitate toward the most convenient option at the time…if you eliminate all the easy ways into your home, they will likely be inconvenienced enough to search for a less secure location instead.