In light of recent zigbee concerns or issues I’ve started to use various device monitor smartapps. They all invariably use events which for a quiet device like the orvibo contact sensor is pretty useless. For instance if the window is never opened then unless the battery level changes there will never be an event and you’ll be alerted to a “dead” device which isn’t.
In order to fix this I’ve added a “heartbeat” event to the device type that occurs everytime (roughly 15 minutes) the device updates it’s battery status. This way we can see if the sensor is still alive of not. Hope this helps as it certainly helped me find a device which stopped talking due to me moving an ST outlet which it was using as a relay! 
Wayne, when one of your sensors is beyond Zigbee range, does the green light stop flashing when the magnet opens/closes the device?
That’s what I’m seeing here.
Is pretty difficult to be sure as I have a good mesh with lots of powered signs devices as relays. But I think that’s similar behaviour with all zigbee devices. On the original ST sensors they would get “stuck” in one mode and need battery reseating. I now have more than ten repeaters around the house hence I rarely get this issue unless I decide to move or change my repeaters.
OK, I can confirm that the green ring doesn’t light if the sensor is out of Zigbee range to the hub. I’d assumed it was a simple send, but there must be a return handshake, and the green ring is an ack of that.
Still doesn’t explain why the Zigbee range in my house seems to have fallen considerably over the past week or so. It’s like the hub has been turned down.
I have one which my new heartbeat feature is helping me work out it is just about on the the battery fringe of range. Not had many range issues until recently too. But I put this down to the noisy 2.4 spectrum.
What’s the devicecheck SmartApp you mention in the comments Wayne?
I should have typed device monitor. There are a few similar smartapps which will warn you when they see a device not having any events within a threshold you define. This way you don’t have any Motion or contact sensors which have fallen asleep without you realising. To be honest I don’t understand why smartthings don’t have something built in that tells you that it cannot see a zigbee device for an extended period. These are they next best thing.
My current fave is the simple device viewer
@PailOckenden -14 is the standard power level for Zigbee in the UK so your hub is correct. i had issues suddenly start with Zigbee devices a couple of months ago. i am unsure as to why they suddenly started, could have been a new wifi point in the neighbourhood maybe? i spend a lot of time doing a site survey of my wirelless devices around and then i havd to change my Hue bridge zigbee channel and move my wifi to a frequency that didn’t conflict which surprisingly is very difficult if you wifi band range is set to 20/40 mhz or 40 mhz
see the diagram below
the wifi channel spectrum is very very wide as you can see, but at 40 mhz its huge. I settled on Wifi Channel 10 with the 20mhz extension above, which takes you upto wifi channel 13 (good for us in the UK as we have a wider 2.4ghz band) and my hubs zigbee is stuck on channel 15, and i changed my Hue hub to channel 11. and i removed my sonos bridge and put my sonos on my wifi as i just had no room for it in the whole band taking into account neighbours wifi also. since doing that its been 100% solid
@a4refillpad thanks for the DH, i just picked up an Orvibo sensor to test with, looks to be working fine so far.
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@a4refillpad The fingerprint worked for me, the sensor was added as Orvibo Contact Sensor.
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Yes fixed that a while back. Maybe I should edit the op!
Makes adding devices much easier 
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Thankyou very much for this @a4refillpad working great here with no issues except banggood’s delivery time 
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Glad it’s working well for everyone. I’ve been having lots of signal strength issues. I wish ST would allow people to change the zigbee channel. I have a lot of neighbours using WiFi channel 1 and it’s killing my zigbee devices. Very frustrating 
You can’t change the zigbee channel on the V1 US hub, but @slagle has previously said that the V2 may change its zigbee channel on its own when it is rebooted. I haven’t tested that to see for myself, but you could give it a try.
So true…
@slagle why can’t we simply be given a parameter to change in the IDE?
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@JDRoberts I can confirm that the V2 Hub never changes its channel on reboot even if you put a conflicting zigbee hub very close it still doesn’t do it. @a4refillpad time to offer IT help to your neighbours and whilst there make up some excuse for the need to change the wifi channel.
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I believe you, but unless I misunderstood, or unless it’s US only, I thought @slagle said it was supposed to change when you rebooted the hub ( not dynamic channel assignment, just randomly picking one channel at start up and sticking with it). But maybe he was referring to something else.
You can change the channel on a Phillips hue bridge, but you have to use the option in their app to do so.
I’ve done similar tests to @Fuzzyligic - two hubs sat next to each other remained on the same channel. Also deliberately put on right next to a wifi router on a conflicting channel and the ST hub stuck to its channel.
I came to the conclusion that they are factory set, and can’t be changed.
P.
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I purchased one of these contact sensors but it keeps just stopping working for periods of time even though heartbeats are being processed, is everyone seeing the same thing still? thinking i will dump it
I saw something similar, but it was a range issue - I was just on the fringe of reception between the sensor and the hub.
Putting in a repeater (and then re-adding the sensor so it paired via the repeater) seemed to fix things.
P.
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I’ve seen signal issues but not yet seen a device which reports a heartbeat not working. I’ve now got 27 of these and apart from the aforementioned issues and some poor batteries (which are cheap to replace) I’m pretty happy with them.