the command is:

set_wakeup()

if you are using the i2c class in python

yes it is… ONY AFTER some time (10 minutes) on rpi2 or rpi0w i2c hangs with THIS sensor.  RPI3 seems to work fine. 
Now after some days of running, same error on the RPI3.  It looks as if read / write to sensor must not happen to frequently, added a wait of 0.08 secs, that seems to help (for the rpi3, not for the rpi0w/rpi2)
 

ps. sudo is not needed for i2cdetect -y 1

use the mute function ==   set_mute_mode(1) with i2c connection and  similar with uart/serial   setting_CMD( 0x83, 1) ==  that will also shorted the dead time. 
Just switching the speaker to external, will block the mic input until the response phrase is finished.

reply to: Martijn.vaB wrote:

….  Alternatively one might use a GPIO connected to the VCC (usually 5V or 3.3V, both suitable for the module) and put that to LOW and HIGH periodically to do a power based hard reset on the SEN0539.

The GPIO can only deliver 10 mA, the module demands 50mA .. 300mA (speaker on, high volume) . That will likely not work

set wake on at start can be done in i2c mode not in uart/ serial mode. 
in i2c mode the command is: set_wakeup(), I tried  self.setting_CMD( DF2301Q_UART_MSG_CMD_SET_ENTERWAKEUP, 0) with 0,1,2,3 none of them works.. 
but you can do the following in uart/serial
say wake word(hello robot),  receive cmdid = 2, then call set_wake_time(255) immediately and every 200 secs after. That will keep awake in ON mode for ever.
 

the speaker range is 1-20, overwritten by setting mute =1 = turn off speaker.
  I tried level 1, 7, 20 and they  give higher speaker output with higher values. 

The comment 1- 7 in the code is likely wrong. I tried this in i2c and uart/serial mode. My test system is an rpi3b with python.
the advantage of set mute on is taht you can start the next command after 1-2 seconds instead of waiting for the voice answer to finish. with this you can eg do “turn on the light” + “set 60 percent” (custom command = 5). then you wait after receive 103(light on) for 3 secs if there is a follow on cmdid =5, then you set the light to 60%.