Canon EOS REBEL T5I Instruction Manual page 99

Wireless Flash
Photography
You can use the built-in flash
for wireless flash shooting.
The camera's built-in flash can work as a master unit
with Canon Speedlites with a wireless slave feature and
wirelessly trigger the Speedlite(s) to fire.
Canceling the slave unit's auto power off
To cancel the slave unit's auto power off, press the
camera's <-X-> button. If you are using manual flash
firing, press the slave unit's test firing (PILOT) button to
cancel the auto power off.
Be Sure to also read the information about wi[e!ess flash ..........
photography in the Speedlite's instruction manual