Dang...the 18% sale on Amazon ended ($269!), now at 8% off at $293. I'll hustle up my mojo and get that sale price back through focused meditation. 
Now that you mention it that does sound familiar, and that's a very popular sensor recently...found them (there are two!) and will add to the OP. Done, added!
That is a great idea...hadn't even thought about that. Nice!
As a note, the Hubitat mount set (that @danabw already posted a link to) also has an option for the Hubitat C4 (plus I plan on adding the C8 to it when that becomes available and I have the proper dimensions).
Plus I also have a set of mounts for Blink camera sync hubs posted.
Updated my description above! Thanks for reminding me about the multiple versions available including C4.
As you know I'm actually using your wall mount with my two C7s and it works great.
I have two more designs for ThirdReality motion sensors and smart buttons that i haven't published yet.
Love to have them listed when you do! The more the merrier... 
Thanks for adding my Yagusmart 4 button desk mount, if you think it’s relevant you might also want to list my 3D printer monitoring and control for Klipper based 3D printers:
Absolutely, yes! Thanks for pointing that out, I hadn't found it.
I guess it’s worth adding the octoprint driver too (not mine)
Thank you for posting the the ThirdReality corner mount 2 link. I like that it can hold the sensor without tape so it can be removed easily for the eventual battery changes. I will be able to relocate the 3rd Reality sensor to the corner where I wanted to put it now.
That was my reasoning for designing that variation; I didn't want to put tape, etc. directly on the sensor.
Two more options for mounting the ThirdReality Motion Sensors or Smart Buttons.
Both of these are for flat surface mounting, one with 3M VHB tape or Command Strips, the other with a small screw.
Tape Mount:
Screw Mount:
I just use this stuff to stick the sensor directly to the wall:
https://www.amazon.com/gp/product/B09RN8JS7W/
Wall mounts for tablets:
Samsung Galaxy Tab A8 (2021)
Samsung Tab A7 (T-500)
Amazon Fire Tab
Edit: More Fire tab mounts
HD 10 2021
HD 10 2021
HD 10 2019
Untested by me (yet).
Entending/swiveling spice racks...a 3D printer WAF win. 
Sliding spice rack from Thingaverse. I only used the bottom part of the design, leaving out the steel rods and the top, as our spces are in a short space in the cabinet and the metal rods and top in the original design would just get in the way for us. Nice side-effect is access is easier w/the rods omitted.
This was a big win...wife wants more.
Modifications: Making the sliding rail 2% smaller than the track allows it to slide easily. I increased the width of the base track by 2%, left the sliding rail at its original width, and increased the bottom (the part the spices sit in) by 2% to match the track. That additional 2% in space allows wider/square spice jars to fit easily.
During "construction." Tracks the units slide in are held in place by two legths of strong velcro:
Slide out to view/access:
Rotate in mid-air... 
Mind blown:
I printed the Fire tablet mount. It's not terrible but it does add quite a bit of bulk.
Yup, this one looks nicer, but of course it's for a newer version (2021) than what I have (2019).
Ah...see, I need the extra space behind the tablet since I ran my power cables through the wall.
Thanks for posting the spice rack link. My wife likes them. I can see me printing up a bunch for the camping trailer as well as the house.
What post/bolt combo are you using?
Something like this that I got at local Ace HW store.
I think it was 15mm size. Called book binding screws I think.
Download the Hubitat app
