I have two ZSE18 motions that I migrated to the C7. When I paired them with the C7 with S0 and S2 checked they were incredibly slow. When I excluded and included them with S0 and S2 unchecked they are extremely fast.
Do I need to use S2 for motions in my house? Are there any performance, privacy / safety benefits using S2?
That's up to you; some people like to, others don't. S0 is likely to be slower than non-secure or S2 communication, but S2 and non-secure should be pretty close, so I'm surprised that the difference is that noticeable. Maybe there's something wrong with the device, driver, or the Hubitat's Z-Wave implementation here. So, to answer the part of your question, there aren't any performance benefits, but the penalty of using S2 shouldn't be that bad (S0 is a different story).
But there are theoretically privacy benefits. Regular Z-Wave traffic is not encrypted, so theoretically someone could be within range of your house and "sniffing" Z-Wave traffic to see if/when motion sensors report activity that could suggest, among other things, whether you are or aren't home. (They could theoretically also send a message pretending to be a controller for devices that accept commands, like switches/dimmers, too, without S0 or S2). S2 is encrypted, making that a difficult task. (S0 is too, but to a lesser degree, and there are known attacks with arguments about how difficult that still may or may not be to exploit in the real world.) You may not care--someone could just look at your windows, lights, garage/car, or whatever and glean similar information, but other people care more about this. I do care about S0 or S2 for some devices like locks and garage doors. I'm still deciding about switches/dimmers and whatnot. Personally, I care less about sensors, but it's up to you!
FWIW, I think Hubitat is one of the first hubs to support S2 (definitely one of the first, if not the first, 700-series hub, which has specific requirements about how security must work), though I know of others like Ring (not really a general-purpose hub) and v3 SmartThings that I think recently added support or will soon. Anyway, my point is that most Z-Wave networks out there probably have lots of non-secure devices on them, since that was the norm for a while and probably still is for a lot of people. Not an argument for not using it, just some history. 
Thanks for that information. I think you're right about the device. I need to take a look at the sensitivity setting. I'm going to exclude / include the motion and uncheck S0. I could have been confusing response for sensitivity.
I have one of these sensors. What are S0 and S2? I am not familiar with these terms.
I troubleshooted this further. I'm not sure if the problem is with the ZSE 18 or the C7 or both, but here it is.
It turns out that when S2 is enabled, the ZSE18 won't accept changes to its configuration values. I change the PIR sensitivity parameter 12 from 4 to 8, initiate a manual wakeup, and watch the log as the value of parameter 12 is changed from 4 to 8 in one line and then back to 4 in the next.
When I disable S0 and S2 the parameter change goes right through and the sensor works more quickly.
The next hub firmware release, 2.2.4 (no ETA), is reported to have some fixes for many S2 Z-Wave devices. I'm not sure if this is specifically one of them, but it's not out of the question. Maybe that will help?
In the meantime, you could try changing the parameter directly with the Basic Z-Wave Tool. I think that's been updated to support S2 devices.
I’m seeing something different from you. My USB-powered ZSE18 in the downstairs bath, on my C-7 with 2.2.3.148, is paired S2 (I just let it pair defaults) and it has instantaneous response running a Motion Lighting app that operates a Caseta switch. In fact, the mesh likes it so much it routes everything through it.
I didn't know about that tool. I may try and just change the parameter after pairing with S2.
My speed of detection is related to the motion sensitivity. I can't increase the motion sensitivity because it always overwrites back to the default in paired S2. Are you able to change the PIR sensitivity? Zen18 firmware ver 1.3.
Yes, and it seems to stick.
What's your Zen18 firmware version? Mine is 1.3.
That is interesting. I'll try another hard reset. Thanks for the info.
I will admit that I haven’t done extensive testing to see whether changing the sensitivity, which does seem to stick, is truly changing it. It’s set on 8, and, before tonight when I read your post and made a quick test, I haven’t changed it since I migrated from my C-5 about 6 weeks ago. If your results appear consistent to you, I could try more testing this weekend to see if I notice a difference changing sensitivity to least sensitive.
Download the Hubitat app
