Canon REBEL T3I EOS 600D User Manual page 267

Using Eye-Fi Cards
Cautions for Using Eye-Fi Cards
If "J" is displayed, an error occurred while retrieving the card
information. Turn the camera's power switch off and on again.
Even if [Eye-Fi trans.] is set to [Disable], it may still transmit a signal. In
hospitals, airports, and other places where wireless transmissions are
prohibited, remove the Eye-Fi card from the camera.
If the image transfer does not function, check the Eye-Fi card and
personal computer settings. For details, see the card's instruction
manual.
Depending on the wireless LAN's connection conditions, the image
transfer may take longer or it might be interrupted.
Because of the transmission function, the Eye-Fi card may become hot.
The battery power will be consumed faster.
During the image transfer, auto power off will not take effect.
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