Sorry for all the questions.
I know there is a manufacturer compatibility list but that doesn't necessarily tell which are any good. There are so many different door sensors out there. Any recommendation on a good one I should get. I suppose a zigbee version would be best as I got some Hue bulbs so that mesh is kinda already there.
People who use just light bulbs in their systems tend to have mesh issues with battery devices. Just as a heads up.
I use iris v1 contact sensors because they are cheap about $4.75 per sensor but I have a lot of outlet repeaters to support my network.
Visonic Mct-350. 5 year battery life, supported by HE.
Can usually find them on eBay for $10-20/ea in the US.
I have these guys everywhere. They used to go on sale for about $11 quite regularly, that's when I would buy them. They never drop off the mesh, but they don't seem to report battery level very accurately (I have had 3 of them reporting 0% battery for months now). The batteries also tend to last wildly different lengths but usually at least a year.
I have never had any issues with this. I doubt it has anything to do with them being light bulbs. Probably more likely the person powers the bulbs off, dropping them from the network.
Many zigbee bulbs are proven to be bad routers, and can actually make the zigbee mesh significantly worse. Typically this is because they allocated too little RAM to the routing table internally, it gets full, then starts dropping packets all over the place.
It is more of a problem the higher the zigbee traffic load is. Packets get dropped, so the device re-sends the packets generating even more zigbee traffic, which makes even more packets drop... Etc...
On the other hand SOME bulbs work fine as routers, so it is not all zigbee bulbs by any means.
To add to the above: while it is great that your personal experience has not noted any problems, this is indeed a widely documented issue with most Zigbee bulbs (some better than others, but most not good). See, among others: How to Build a Solid Zigbee Mesh - Hubitat Documentation
So, reading that post says about mains powered devices acting as a repeater. But bulbs are and they can give problems. Are there any recommended devices that repeat better than others. I don't mind buying a plug or 2 to make sure the mesh is good, but don't want to buy something where I still get issues.
Also, and I know this is opening pandoras box but, is it better to go Z-wave? I'm going to buy a smart lock and they offer the option of zigbee or z-wave but I don't know which I should get.
peanuts are $10 and so are ikea's outlets.
 The $10 peanut sale is over
Anything mains powered, zigbee, and not a bulb should be fine UNLESS you are using Xiaomi brand devices which require specific repeaters to work.
Both zigbee and zwave have strengths and weaknesses. Nothing wrong with zigbee, nothing wrong with zwave. A poorly designed device in either case can cause havok.
The Ikea plugs are cheap enough for me to get a couple for the house.
Back to the original topic, this visonic ones are mighty expensive here in the UK, over £30. Too much considering I'm buying 4 along with smart lock, doorbell and hubitat. I'll probably go with what Helena7t7 suggested and replace with better when the others come on special
Sigh, no cheap sensors available this side of the pond (UK). The cheapest I see are Xiaomi-Aqara. While they seem to give some problems, they are listed as working through the Ikea plugs, so will give them a try.
Thanks for all the help.
Your explanation makes sense to me. I was certain that Lightify bulbs weren't making my zigbee mesh unstable because they were being turned off. This explains why things got worse as I added more zigbee repeaters and zigbee end devices - rather than better.
The aqara humidity/temp sensors are supposedly very fickle about what hubs and devices they'll work with, but IMO they're with it. These give me a very rapid response to changes in humidity and temperature so they probably make the best sensors for controlling extractor fans.
Curious, how come nobody mentions the ST multipurpose v5 sensors for doors? They seem to work well for me so far. Anything I should be aware of about them before they pass the return period? I'm also using one as a garage door tilt sensor, and no problems to note so far. I've had just one of them falsely report an open window, but its contact with the magnet isn't that good due to the window being recessed relative to the frame, making the magnet stick up a bit (appearance wise, this doesn't bother me.)
Ok, I can either save some money (and by that I mean at least half - over 50 bucks) by getting Ikea plugs as repeaters and the xiaomi devices or I saw on ebay I could get the visonic 340's (and some other stuff) for over 100 (used). I'm leaning towards saving the money for other gadgets and hoping the Ikea plugs will save the day.
Am I being stupid and should spend the extra to save me hassle or will the Ikea plugs mean I don't have to worry?
Literally the only thing I have are the ikeas, and I haven't even seen a hint of a problem yet, though I'm using the environment sensors, not the door sensors (for that I'm using the ST multipurpose v5 sensors.)
How many Ikea plugs do you have? Like, is your house flooded with them or just a couple strategically placed?
Just a couple (literally two) strategically placed, though they don't have to reach far as my house is only 1902 square feet. My entire zigbee mesh consists of 6 ST multipurpose sensors, 10 iris v2 motion sensors, 1 hue outdoor motion sensor, 3 ST leak sensors, 2 ikea tradfri plugs, and the 4 Aqara humidity/temp sensors. Doesn't include the Hue zigbee mesh, which is on its own separate controller (the hue hub.) That mesh has 16 Hue bulbs, one Lutron portable dimmer, and one Hue four button batteryless remote.