This Sample tip from EASYDSLR Course – http://easydslr.com gives you the answer.

My Vote for the most dangerous setting in the DSLR menu system is… *insert drum roll*

• “Release shutter without card” (DISABLE this) in Nikon DSLR cameras it can be hidden in the custom functions as “Release enable”

Format and Delete on your Digital Camera are certainly dangerous too. But they are more obvious – the reason I chose the above feature is because a lot of DSLR owners may not realize it’s an option.

Imagine the dread after you finish an important shoot – like your best friend’s graduation, or worse, a destination wedding ceremony – and reach in to grab the memory card and find that the slot is empty – YOU HAVE NO CARD IN THE CAMERA!

That is what that setting can result in. Sure – you get warnings popping up on the LCD but I know that in those situations 90% of the time you are looking through the viewfinder not wanting to miss a single moment.

My advice (ignore at your peril): Make sure it is DISABLED on your Canon and set to “Release locked” on your Nikon (this is the Default for Custom setting no. f4 for the Nikon D5100 for example).