9 Ways to Customize Your Canon Rebel t5i
Prevent shutter release without a memory card.
By default, you can take a picture without any memory card in the camera. That means when you press the shutter button, the camera will release the shutter to take a temporary photo that it stores in its internal memory. The picture appears on the monitor for a few seconds but then disappears and can't be retrieved.
If you’re wondering about the point of this option, it’s designed for use in camera stores, enabling salespeople to demonstrate cameras without having to keep a memory card in every model.