hi - please speak to me like I am a young child- this is all new to me.
I've paired a sonof SNZB-04 contact sensor to my C8 hub and it seems to be falling into sleep mode.
I have it set to alert me when the contact is closed state.
I dont really understand how to interpret the logs -or 'ping' the unit to see if it's still alive etc.
It's going to be used to tell me when I need to replace my water softener salt - but I dont understand why it is falling asleep.
Can someone please tell me what I need to be looking at. I am looking at the logs and I've enabled 'debug logging' but do I need some repeaters because my hub is on the floor above and the sensor will be downstairs? It was working perfectly last night but I was repeatedly triggering it so it was 'awake the whole time.
I may not necessarily be able to help with your device issue... But a couple of things to confirm would be the driver you are using for the sensor in Hubitat and the platform version you are running on the HE hub.
The question I would have is what makes you think it is falling asleep? Is it that the physical device is opening or closing and that is not being reflected in HE?
To explain some basics of what you are seeing in your screenshot of the logs... The Information log entries are what you would expect, logging state changes like opening or closing in this case. The "updated..." entries are likely when you have hit Save Preferences on the device page. The warning logs are indicating when logging settings are changing, including a common 30 minute timeout after you turn debug logging on, just to keep these logs to a minimum without needing to remember to turn them off manually after some troubleshooting.
A tip, in case you were not aware, you can click the "warn", "info", etc part of the log entry to open the device or app the log is for.
SONOFF SNZB-04 is one of the most difficult to troubleshoot Zigbee devices.
It operates in a 'deep sleep' mode all the time, the only exception is when it is paired to the hub, when the contact state changes or when the battery level is reported (battery reporting is problematic too). It is not possible to ping it or to know in any other way if it is online to the hub or not. A few white hairs on my head are because of this sensor..
My advice will be for critical applications (like monitoring salt levels..) to use another contact sensor.
You can still use the SNZB-04 for less important applications, preferably closer to the hub.
ok so all contact sensors are not equal then clearly - I can return it. I only got it yesterday,
What sensors would you recommend that are more liable to stay awake?
I am thinking also of adding some repeaters just in case the signal path is messy. All my bulbs / groups that run through the C8 are working fine and there's bulbs in the same room as the softener is - they're hue / innr but I'm guessing that wont help with the Zigbee.
It all depends where are you located - US and EU/AU Zigbee device availability is different...
This is the right approach!
You need to build a strong Zigbee mesh, by adding mains-powered zigbee devices - always-on plugs/sockets as an example, but never Zigbee bulbs that may be turned off.
You can also check this thread :
but the solution there was more of a complex workaround...
When I bought my first device (Kwikset 914 lock) to pair with HE, it was flaky, even though it was less than 6 feet from the hub. Once I added a repeater, the lock functioned correctly.
My hue bulbs go via the hue hub then an integration on the C8.
The scenes/groups are added to my C8 only not the individual bulbs because I have a lot of them. I have 2x hue hubs (upstairs and downstairs) and these do their job fine. (most of the time)
I'm gradually integrating the C8 and using the Alexa boxes in the house as an end point for things like announcing stuff and turning on and off the light groups (via the C8 Alexa skill)
The contact sensor is my first device that is paired directly to the C8.
I will get some repeaters even though I am not really having signal issues with anything running through the C8 other than the Sonof contact.
The bulbs and any other devices paired to the Hue bridges form their own Zigbee mesh separate to the one setup by the HE hub. So if the contact sensor is the only Zigbee device paired to HE, then it will be communicating directly with the HE hub, and the lights will play no part in the communications with HE for the contact sensor, nor will the Zigbee setup on HE affect any interaction with the bulbs on Hue (apologies if I'm explaining something you already know).
But to contradict that last statement .... One other thing to keep in mind, which may or may not be playing a part (more likely the device from @kkossev 's comment earlier).... When running multiple 2.4GHz networks, including different Zigbee mesh networks as well as any 2.4GHz Wi-Fi networks, it is important to make sure the channels used do not interfere with each other. There are some posts here on the Community or you can lookup online more generally for some recommendations on channels that you may want to use.
It may be what Simon says - a WiFi interference with the Zigbee channels that you may need to find and resolve (by changing the Zigbee channels).
Philips Hue bridges usually have rock-solid performance - I have one Hue hub controlling probably 20 bulbs all over the house and it never misses to switch a bulb on or off.
This also caught my eye.
Is it going to be problematic? Can mount it higher up and run a usb extension to it.
Deal of the day: SONOFF Universal Zigbee 3.0 USB Dongle Plus ZBDongle E Gateway with Antenna for Home Assistant, Open HAB etc, Support Data Flow Control https://amzn.eu/d/4sU9e0j
Ok, cool, I've got one myself that I'm not using, but don't have a need for it as a repeater. The flashing was a little painful for the other one I am using as a coordinator for Z2M (one's a P and one's an E variety from memory), but once you get the hang of it, it's ok...
The last 2 Amazon links are for the same Zigbee repeater at a much better price - get at least one of these. When installed in between the contact sensor and the HE hub, it may turn out that you don't need another sensor.
The Third Reality contact sensor is used by many HE users (mostly in the US), so it is a good choice also.
The Woolley plugs (rebranded Sonoff) were reported by one user to have some issues in Hubitat, although they worked with a custom driver.
Perfect thank you - I'll get one of the USB dongles - use it with an extension cable and power from an old USB iPhone plug and mount it in the room below my hub.
Are these best mounted high up - or possibly as close as I can get it to the contact sensor?
There is no need to mount the Zigbee repeaters high up - there are a lot of reflected radio signals around, so the height is not important, but it will be good if there is some free space around...
The Zigbee repeater (Zigbee router) is better to be positioned in the middle distance between the HE hub and the battery-powered device.
One other thing to keep in mind, which may or may not be playing a part (more likely the device from 
