How to use your external camera's motion 
detection with ZM


Contents
1 Background
2 Core Trigger Architecture
3 Requirements for Triggering
4 Quick test
5 Implementation Strategy
6 Source code
7 Notes
8 References I found useful



Background
Zone minder has an awesome 'trigger' architecture which allows any external
event to trigger a recording on ZoneMinder. This section explains the basic
architecture and then goes on to describe how you can use your own camera's HW 
motion detection to trigger a recording on ZM. You can replace this 'trigger' 
with any other event - such as, for example, triggering your ZM recording when 
say your Nest thermostat goes to Away mode. The options are limitless



Core Trigger Architecture
	

If you enable OPT_TRIGGERS in Options->System, then ZoneMinder starts a process
called "zmtrigger.pl" (/usr/bin/zmtrigger.pl). This is a perl script that 
basically offers an easy to use interface for anyone to send it commands to its
default TCP port (6802) to initiate/stop recordings. Note that zmtrigger also 
offers other means of IPC - I just found the TCP channel easy and reliable.

zmtrigger does not care what caused the event. All it is waiting for is a simple
text instruction from anyone capable of sending a command to port 6802. So what
that means is I can write any program that monitors anything, and when my 
program thinks something happened which warrants a recording, all I need to tell
zmtrigger is "please record monitor 3" (and optionally specify more parameters)



Requirements for Triggering

OPT_TRIGGERS need to be enabled
Prior to ZoneMinder v1.30.2, the monitor mode MUST be set to Nodect (ZM 
won't initiate recordings if in any other mode).


(To combine both ZM normal recording, and say external triggers, with ZoneMinder
prior to v1.30.2 you can always add two monitors pointing to the same camera - 
one in say modect and the other in nodect and use the latter one for external 
triggers)



Quick test
Lets assume you have a monitor id of 1. As a quick test, just try this telnet 
zm_ip 6802 And when connected via telnet simply type in
	1|on+20|1|External Motion|External Motion

You should see ZM create a new recording for Monitor ID=1 for 20 seconds with a
name and cause of "External Motion"



Implementation Strategy

Foscam's CGI document shows that if the camera's motion detection is enabled,
then when it detects motion, you can use the getDevState command - if the value
of XML tag  is 2 then motion is detected. It resets back to 1 if there is 
no motion detect
Unfortunately, Foscam does not support posting events/callbacks when motion
is detected. Note that there are cameras that support web hooks for motion 
notifications, like Axis cameras.
so I need to poll it once every few seconds and check this value
If this value == 2, send a record request to zmtrigger (and thanks to ZM's
ring buffer, I won't miss the image that caused the alarm)



Source code
Here is the code to do just that (and some other checks for optimization) It
loops through all my cameras and sends triggers when motion is detected
zm_foscam, 
looks like I deleted that repo by mistake. I don't have a copy. But looks like 
someone else took that code and improved it - see his repo here. 



Notes

Your imagination is the limit here - you can create triggers for any thing
you want - ZM doesn't care what the trigger is. As long as your script tells
zmtrigger to start/stop recording and for which monitor, that is all ZM needs
I initially used my camera's HW motion detection for a few weeks, after 
getting frustrated trying to configure ZM's own zone system, but when I 
understood how to use ZM's own zone detection, it was better.
If you are worried if this constant pinging of the foscam may slow it down,
it does not. I used it for weeks without any problem




References I found useful

http://www.sparxeng.com/blog/software/zoneminder-network-triggering