why dbus-monitor can't catch method call?

[Galaha Shine]

Hi,


I start dbus-monitor with `dbus-monitor --system`, then `I try dbus-send
with dbus-send --system --print-reply --dest=org.bluez
--type=method_call /org/bluez/audio org.bluez.audio.Manager.ListDevices`

I get the correct reply as below:
method return sender=:1.23 -> dest=:1.42 reply_serial=2
   array [
      string "/org/bluez/audio/device0"
   ]

But the problem is nothing caught by dbus-monitor. 

I've try dbus-monitor --session, it doesn't work yet.

My dbus-monotor is 1.1.20 without x11.

Regards,
Galaha