Is there any way that i find out the monitor which connected by HDMI is on or off?
AIUI, that's probably true for HDMI/DVI "DMT" based monitors/displays but AIUI, but am not certain of the details, that T.V.'s that use HDMI "CEC" based methods support some bi-directional communication through the HDMI port, but that may be only to provide "remote control" signals rather than T.V./monitor status.MajorMuff wrote:As far as I know the HDMI port only serves as an output. To read the state of a monitor it would need to be an input as well. I might be wrong on this but everything I can find online does suggest this isn't possible with a Pi.