NERDS ASSEMBLE!!!
Continuing on the theme of Let's talk creative uses for _____ sensors. This time let's hear some of your creative uses of contact sensors. Nothing is too weird or wild so get the creative juices flowing and share with your fellow Hubitat enthusiasts. Theoretical discussion is definitely encouraged.
Previous discussions:
Lux Sensor
I don't think I have any real neat uses for contact sensors as of yet. The only thing that is a bit different is using a contact sensor for my in house mail slot. It originally worked terribly and tried every other type of sensor to make it work until I discovered you do not need to use the included magnetic side of the sensor. Swapped out with a small rare earth magnet (Much more powerful and longer reach) and BAM, near 100 percent accuracy. Than set up a notification to announce on my Echos and on my phone. This crushes my security camera in notification speed.
I use a contact sensor to sense when my HVAC blower turns on or off and adjust the Sonos volume in the following manner:
Years ago I built an outdoor pool shower. The shower head was over the lawn and what's the point of a shower if your feet get dirty because of the shower splash at your feet? So I bought a bamboo mat and decided it would be the trigger for the shower itself. Stand on the mat, the shower turns on. Cool.
I got a pressure resister and wired it to the contacts of a contact sensor. I mounted all of that under the mat, protected from the water by a sheet of clear lexan. Standing on the mat caused the pressure resister to be "pinched" between two pieces of wood. That was enough to trigger the contact sensor which in turn opened the shower valve.
It's all gone now because the bamboo wooden mat didn't last in the sun. It was placed on the lawn under the shower on those active pool days then picked up and stored outdoors when the pool was not active. Eventually the sun plus rough handling caused it to break up. The bamboo... not the pressure resister & contact sensor. That would work today if I put batteries in it 
I have one on my milk container in the integrated coffee machine, google gets more angry the longer we leave it in there.
One on the loft hatch door for the loft lights not interesting but makes me happy
Well, I put one on the front inside of the litter drawer on my Litter Robot, which uses the integration that Dominick Meglio (@dman2306) ported from SmartThings. One Rule, inspired by Jared Zimmerman (@jared.zimmerman), turns the bathroom vanity undercounter lights green, yellow, red depending on the level of cat poop in the litter drawer, and another Rule flashes the vanity undercounter lights if an alarm condition (e.g., litter drawer needs emptying) occurs. The contact sensor on the litter drawer triggers a Rule that resets the drawer gauge if the drawer stays open for more than 30 seconds, as occurs when the litter drawer is opened to replace the dirty litter bag. This means that the Litter Robot app never has to be used.
I use a modified door sensor to tell me when my garden watering system turns on.
I replaced the Reed sensor feeding it with the pump activation relay of the system. (The pump is pressure activated, not by the relay.)
This notifies me through HE we the garden is being watered, and if the pressure pump does not activate when expected to do so.
(Here water is extremely expensive.)
I put one on the trigger valve for a water-powered backup sump pump. It notifies the owner that the primary pump stopped working. If so, then the contact should cycle open closed as the backup works. If the contact stays closed, then it warns of a possible flood condition.
I am working on a system where a wall mounted RGB light turns on certain colors to tell me the car is pulled far enough into the garage. I am using a SecoLarm beam sensor that has NO/NC outputs tied into a Ecolink sensor that has external input terminals to get the status into Hubitat. The hardware part is done and works.
The rule is what is holding me up, I just haven't been inspired to make it actually work, there are quite a few conditions to the rule and it gets complicated fast.
I don't want the RGB lights on all the time, I want them initially turned on with the garage door open, and off after the garage door closes. I want the color to change on the RGB (flip between say red and green) as the beam sensor is blocked or unblocked. Red as you are pulling in, and green once you clear the sensor. Similar to the first condition, I don't want the indicator to come on if the garage door is shut and I trip the beam for some reason like getting something out of the car.
About as creative as I can get is when my Tempest detect rain it will check all the window sensors and alert us there is a window(s) open and and to close it... (still working on the rule)
I have the same as @rlithgow1 - Tempest rain triggers Alexa to tell us to close windows. It also checks the wind direction and notifies us to close only those that really do need to be closed (west facing windows only if the wind is coming from the west). It’s not yet perfect, but working well enough!
My backup sump pump system has contacts to integrate into a home alarm system. So I wired in a zigbee contact sensor instead. Now if and when my backup system ever has to engage, I will be immediately notified.
Recently I had to replace my mailbox. Or more specifically my plumber had to replace my mailbox since they ran over my old one. I took it as an opportunity to wire up a contact sensor. I used a cheap reed switch and ran wires to the sensor itself which I was able to stash inside a housing in the mailbox post. Ended up being pretty stealthy! Had to put the sensor in the post because the new mailbox was waaaay thicker than my last one and signals just wouldn't go through it.
Must be nice to not have wood framed crank out windows. With the them the windows have to be closed before the tempest was even manufactured to avoid water damage to the damn windows. Seems like just thinking about rain ruins them.
@csteele I don't know if something like this could be used to signal a car was actually in the garage or not. I've seen other posts of people wanting a bulletproof way of knowing if a car was present or not. How exactly did you do your project?
Sliding glass door lock status: I've mounted contact sensors on three sliding glass doors to tell if they are locked or not. The sensor is mounted on the glass and the magnet is on the locking lever. When the lever is in the lock position the contact closes. When that and a second contact sensor on the door tells me the door is closed, I know the door is closed/locked.
Cooktop safety: I use contact sensors hidden in my cooktop that tell me if any of my stove burners are on - if any are on an LED strip at the cabinet baseboards lights up red. When any burnder is turned on it also turns on the under-cabinet lights so we have task lighting.
Outside Electrical panel: I have a contact sensor on my electrical panel to remind me if I leave it open (HE also notifies me when it is initially opened).
Fridge/Freezer door & temp: Contact sensors on fridge and freezer doors to remind me if they are open too long...not really creative, but important. Contact sensors (and I also use a button in one case) in fridge and freezers to monitor temps. (I had some extra contact sensors that do temp, so using them in the freezer allowed me to make use of them.)
A Sengled contact sensor and rare earth magnet make a DIY door lock position sensor for a lock that cannot be replaced with an automated one.
Did you put magnets in the knob and mount sensors under them? If not please elaborate, I can't imagine how else it could be done.
I have a usb lead with the power wires connected to a small 5V electromagnet that is placed next to a samsung multipurpose sensor. It is plugged into a USB port on the TV so I know when the TV is on or not.
I had to resort to this as the TV is a Samsung and none of the IP controls I have tried could accurately and reliably detect when it was on or off. I could have done it by monitoring the TV power but I had a spare sensor and I thought why not?
Unfortunately the USB port remains powered for several seconds after the TV turns off, presumably to allow any connected HDD to spin down, so its not instant for off but it works.
Some creative ideas here. I know contact sensors aren't glamorous and such but some really good ideas here. Anybody have some less than practical waaayyy out there ideas?
Here's a really stupid idea how about a contact sensor on a ceiling fan. That data though probably too fast could trigger a trippy seizure causing led exhibition using a freaky long rule machine integration.
I have one that I have not figured out how to implement it. I have a tall case clock in the foyer and I would like to be reminded when it needs winding. A contact sensor and a magnet on the weights could be used to alert me, but of course I would have to rig it in such a way that it would not be visible.
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