The sound bar auto-powers off after 15- minutes of no signal from the input source. To wake up the soundbar from this standby mode, you would simply need play any content then increase or decrease the volume via the TCL Roku remote.
Note: Another reason the unit may power off by itself can be a power surge or when the power goes out. When the power surge ends, or the power cut out is over the sound bar will reset its self to standby mode.