[Updated with a warning] Hack a Samsung SmartThings Multi Sensor V5

Just bought some of the new SmartThings multi sensors on sale, so I thought I'd share how to open them and hack them to be dry contact sensors.

You can probably use thicker wire than I did, but it might be very difficult to work with and not get any loose strands contacting other points. Plus routing it under the board and out the top would almost be out of the question if you use wire that is too thick. I use wire-wrapping wire that comes in a dispenser with a cutter and insulation stripper built-in. The dispenser is great. You pull some wire out and press a button to trim off a piece. It has a little stripper built in too. Just lay the wire in it and pull, and it nicely strips off a bit of the very thin and flexible insulation.

[WARNING] Seems just 24 hours after hacking this sensor, the battery is dead. This could have been a defective battery or it could have been dead on the store shelf, but this is unlikely since they use a pull tab on the batteries and this was a sealed unit with the battery pull tab installed. Unfortunately, I did not test the battery before installing, and didn't pay attention to what the driver in HE was showing for the battery level.

Not sure why this is happening. there is no contact on the points normally, but I was testing a door open rule on my Microwave, but then forgot about it for about an hour with the door left open (obviously there was a problem with my door open reminder :wink:). So these contact points shown here had been engaged for an hour straight. That obviously wouldn't be an issue for the internal hall effect sender when the magnet is engaged, but it may be an issue if shorting the contact point shown below to ground.

I'm going to change mine over to using a power adapter so I don't have to worry about it, but I just wanted to give a heads up that this might not be an appropriate hack of this sensor if you're running on battery power. If anyone does this modification and wants to sacrifice a CR2450 to test, please post your results here.

Opening

Slide the battery cover off and using a nylon spudger, push it into the space between the grey bottom and white top of the sensor.

Push straight down with the spudger. As the taper of the spudger widens, it will force the top cover/battery holder up and away from the bottom housing.

Don't pry up with your hands or you might break the case! Use the spudger to pry at one side and then the other until the clips on the sides are free too.


Now that the side are free, you need to pry gently at the flat side of the housing and the top will come off easily. There's a small indent you can insert the spudger into.


Once the cover it removed, just grab hold of the spring and lift the circuit board out of the housing.

The Samsung SmartThings Multi Sensor v5 does not use a reed switch. Instead, they use a hall effect sensor. Solder one wire to the hall effect sensor and the other to the ground point as shown here.


You can either choose to drill a small hold in the flat side of the grey bottom housing to route the wires out of the case, or you can carefully fold them backward, ensuring they are sitting as flat as possible. Be sure you are not shorting any other points on the circuit board if you choose to do this

It's a tight fit between the circuit board and the housing, but there are gaps you can use to route the wire out of the case without drilling. Carefully shift the wires over toward the antenna and there is a gap you can use to bring the wires around to the top side of the board.

Reinsert the board into the bottom housing, ensuring that the wires stay within the gap between the circuit board edge and the housing so they are not crushed and severed. I found it best to first insert the board at a slight angle where the wires are emerging, rather than trying to insert the board straight down into the bottom case.

Now feed the wires up through the battery holder of the top housing and ensure the wires are within the gap as shown, then push down on the top cover until it clicks back into place. Then reinsert the battery


Feed the wires toward the dip in the top housing and reinstall the battery cover. Be careful that you do not crush the wires with the tab on the battery cover as shown here.

For now I chose not to convert this to battery-free, but while you're in there, you could easily do that too. I use these step-down buck boards for the job. Choose 3v output with pins or w/o, your choice of course. Use the 5v output from any phone charger and you'll get 3v output for the multi sensor.

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@Navat604
If you have a Lutron Caseta, I modified a pico for that:

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Sorry I don't. I do have a contact sensor for my doorbell. It's a Xiaomi Aqara, not a SmartThings Multi Sensor v5, but it works great. There's about 15 feet of CAT 5e between the contact sensor and the doorbell button. Plus I came up a bit short, so there's an RJ-45 jack connecting that last few feet. I have another ST Multi Sensor I could test later if you like. What's the resistance you're targeting?

Where?

Thanks

Canada only, and the sales already over. Sorry man. Canadian's don't usually get a break on these devices.

I put a 15 ohm resistor on the second sensor and it didn’t react, then I put an 11 ohm resistor on it, and it closed. So somewhere between 11 and 15 ohms is the cutoff.

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[WARNING] Seems just 24 hours later the battery in the Samsung SmartThings Multisensor is dead. This could have been a defective battery or it could have been dead on the store shelf, but this is unlikely since they use a pull tab on the batteries and this was a sealed unit with the battery pull tab installed.

I will update the original post with the warning, but I'm not intending to risk burning through another CR2450 to test this. If there are any takers, I'd be pleased to know the results you have. Not sure why this is happening. there is no contact on the points normally, but I was testing a door open rule on my Microwave last night, but then forgot about it for about an hour with the door left open (obviously my rule wasn't working at the time). So those contacts were engaged for an hour straight. That wouldn't be an issue for the hall sender when the magnet is engaged, but it may be an issue if shorting that contact to ground like I'm doing here.

I'm going to change this one over to using a power adapter so I don't have to worry about it, but I just wanted to give a heads up that this might not be an appropriate hack of this sensor if you're running on battery power.

any update... on the battery issue...
how about remove the hall effect IC?
as it would output high with no magnet, and your connecting it to ground
if open drain there would be a pull up resistor, and when you connect to gnd..
small current should flow... could check the current...

I never ended up trying again with a battery. Both the sensors I have are being powered by a 5v supply with a 5v to 3.3v buck converter. I've not had any trouble with the one I'm using for tracking my dryer, but the one I have connected to my microwave door/light drops connection on occasion. It might be due to the microwaves at 2.4 GHz interfering at the time the sensor is trying to check in.

I think these are good sensors, but the primary reason I bought them was they were on sale and I could get them immediately. I don't think I'll buy any more though. Conversions for use with a relay or conventional button are easier with the Xiaomi Mijia sensors. I have two Xiaom gateways linked to HE via Homebridge. This works very well and their sensor when joined to either the Xiaomi Mijia or Aqara hubs are very stable. Using other sensors, (for me) makes little sense.

i can get them at a good price too...
but i need 1 to be "wired" but still want to power by battery
i might do experiments... yank that hall ic out...

those Xiaomi ones, they zigbee and just pair to HE?

They’re a proprietary Zigbee. They pair, but stability is a problem. The Zigbee network cannot have any incompatible repeaters, and even still, they are a pain to keep paired.

When you pair them to a Xiaomi gateway, they are rock solid.

ok, thats not practical, 2 hubs :slight_smile: for just a zigbee sensor turned wireless
need to find one that i can modify... key is small.. like the samsung

No, you misunderstand (sort of). I have two Xiaomi hubs because I wanted to have two, not because I needed to have two. The second I'm using, but only because I wanted to test it out to share my findings with the community if anyone is interested in linking the Xiaomi contact and motion sensors the same way I have. It's the latest Gateway from the Xiaomi Mijia line and it's only $25.

However, The way I have things connected, it does sort of require 3 additional "hubs". The Xiaomi hub (which is HomeKit native), then an always on computer running Node.js for Homebridge, then an Apple TV 4 for HomeKit automations.

There is one specific Mijia hub that lets you do a developer hack and use an app called MiConnector to get the devices that are paired to the specific Mija Gateway, to then show up on HE directly, but it also required an always on Node.js computer. Setup it not as simple as the HomeKit route, despite having few components and not requiring you to already be an iOS or MacOS user.

For me, Homebridge and Apple TV 4 existed in my house before I bought my Xioami Aqara HomeKit Hub, so it was only a $45 investment. I also already had Node.js running for other things and thus already had an always on computer. Then I just link virtual switches (shared in HomeKit via Homebridge) to the real Xiaomi devices that show up in HomeKit thanks to their newest hubs being HomeKit compatible. This means that I now have very stable contact and motion sensors, that are really small for around $12 to $15 each.

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Bought Visonic Mct-340 E ZigBee Wireless Door Window Sensor off Ebay for this purpose and the battery is holding up... but I worried about it chewing through batteries so I bought Xfinity XHS2-UE upon reading about it's larger battery.

Have not yet modified it for service yet. Both of these require soldering to each side of the magnetic reed switch. I think it was in our community or over in the ST community where I originally saw this done.

I think the idea of careful modification for a wired application is good. It's just the battery life on so many of these that is problematic.

ok.. update... i removed hall effect IC... 72hr later, battery at 99% (wire been closed)
so far so good, i have another samsung sensor being used as a siding door monitor... and i installed it same day, and its at 85% (no modifications, using magnet) oh and this door is open/closed many times/day
so it seems these things use battery quite a bit when there is activity
another day, and i open the wire on the sensor and watch battery...

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update... more days gone by... battery still at 99%
so... now i opened my loop... will check in a day, then few days..
but i think removal of the hall effect IC is the trick

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update... the input to the microcontroller wasn't stable when the loop open, I added a very weak pull up resistor (100k) now have some stability... as for battery its now at 85%... which is what they seem to drop to, after a few days of use... its the same as my unmodified sensor that i put into use on patio sliding door

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Does anyone know the part number or have the data sheet for the Hall Effect IC Sensor?

Follow up info for others that might try to pair the XHS2-UE.

No problem finding it in pairing process but the Generic Zigbee Moisture Sensor driver was auto configured. I had to explicitly select Generic Zigbee Contact Sensor driver. So far so good.

FYI here was a spinoff contact sensor hack that this thread prompted. Thanks to the initial poster.

The points that I show should be the same as what you have. The Base of the sensor should be ground. If you take a multimeter to it, you can confirm that. I don’t have one of those sensors handy to test.