Hi, the only sensor I haven’t yet used from the ST kit is the multi sensor and I’m after some ideas and guidance about how people are using it. I’ve read lots of views on these forums about it being too sensitive and not really useful as a door/window sensor which is a shame because I could have found a use for it in that context.
How is everyone using this sensor?
Because it has an accelerometer, it is commonly used for situations where you want to know if the sensor itself has moved or even just been shaken. People use them as a tilt sensor, as a tamper sensor on a locked cabinet, as a vibration sensor to tell when the washer is done, as a knock sensor on a door (although that one can be iffy, it depends on the material of the door), and one of my favorite applications, inside a cube so that you can tell which of the six cube faces is on top. That lets you create a remote control with six positions. That one is popular for color lighting scenes. 
I haven’t heard complaints of it not being useful just as a plain open/close contact sensor, rather just that it tends to be more expensive than a simple reed sensor so people are more likely to use it for the accelerometer features and buy a less expensive open/close sensor for those uses.
But if you have an extra one, it should definitely be fine for notifying you if a door or window is open, it’s no more sensitive than any other open/close sensor. The sensitivity issues, again, come when you’re trying to detect the sensor being shaken since it’s not adjustable. Some people have tried to use it as a glass break detector, and that’s when the “too sensitive” comments usually appear since just wind rattling the windows will set it off. But as far as the two pieces being together or apart, that should work fine.
Ah yes I have seen that colour cube idea which is really cool. I just don’t have any hue bulbs in the house.
Good point though about the door/window functionality because it’s simply got to align the two parts. I didn’t think that it shouldn’t create any false alarms. Guess I’ll go down that route then.
I know there have been a number of reports in the last couple of months about smartthings motion sensor reporting incorrectly, and in particular some issues with battery reporting. I don’t remember seeing those about the multi sensor, though.
There’s a whole separate set of issues where some of the sensors report is being unavailable or off-line when they shouldn’t be. i’m not sure what’s going on there, you can check the forum threads for discussions. But those images of been reported with different brands as well.
I just wanted to mention that because there’s a difference between using the sensors for convenience notifications and trying to use them for an intrusion detection system.
Without getting into the details I had a bunch of spare multi sensors from buying 5-packs when they were on sale for projects that ended up not being needed. Recently I removed my security system and moved the hardwired contacts over to SmartThings but had two wireless window sensors that I had to replaced. Used my multi sensors on both windows and a third just for open/closed since I had them and for security I wanted a device that ran locally which those do.
Besides open/close and temperature for a room I use these sensors on my front door to alert me if someone knocks on the door, on the mail box slot to get an alert when mail arrives, as s tilt sensor on my garage door, on the housing of my door bell to alert me, to check if the kids open the medicine cabinet… and the fun cube mentioned above (I recently started using the cube to set TV channels using a harmony hub).
The sensors are a bit pricy compared to other open/close sensors but I found them to be really reliable and the vibration and orientation function makes up for the price (they go on sale for 20% off every couple of months now).