Cheap contact sensors (~$20) with external switch "capability"?

Hi All,
I’m looking for cheap z-wave/zigbee contact switches in the ballpark of 20 bucks, with the possibility of adding an external switch. I’ve got quite a few projects in my backlog requiring this, hence the price focus.

I know some sensors have terminals inside, yet I personally don’t mind a bit of soldering if so required. I’ve tested a few devices myself, looked around on the forum and other places to get an idea what’s out there.

The one’s I’ve tested includes
Samsung’s own multi sensor and Iris Contact Sensor Gen 2: both appear impossible to mod, as there is no reed relay. All sensors seems to be in the chip.

Monoprice’s HKZW-DWS-01 seemed perfect, as it’s got both a relay AND a mechanical tamper switch which could be repurposed too. Unfortunately I’ve had a couple of poor experiences with this particular model: One I had sucked the two AAA batteries dry within 48 hours. The other I had kept dropping off and becoming unavailable for no reason. If anyone knows how to solve the power drain short of adding an external psu, I’d be happy to know.

I’ve seen the following sensors mentioned on the forum. They seem able to do the job, yet a bit outside the price bracket I’m looking for as they are currently about $34-37 currently on ebay and amazon.
Schlage RS100HC V N N SL

Others seen on ebay, not tested:

Neo CoolCAM - Interesting as they can be had for about $18 on ebay.
In the review here although the reviewer doesn’t mention it, I think I can spot a reed relay under the circuit board. Anyone have experience with this one?

Sercomm SZ-DWS04 - Equally interesting as it currently clocks in a hair under $20 on ebay
Accoding to this guide on battery replacement, it clearly has a Reed relay inside. Anyone have experience with this one?

If you have experiences with other sensors, I’d love to hear about them

I don’t recommend buying anything electronic off of eBay. A lot of it is counterfeit, a lot of it is mislabeled, a lot of it is used being sold as new. And many manufacturers will not honor the warranty if you buy it off of eBay because they consider it used no matter what the seller said.

So yes, it’s going to be challenging to hit your price point unless you happen to find something on sale.

What you are looking for is a device that has “dry contacts“, right?

In that case, there’s an existing thread for those:

Among other devices discussed in that thread is the monoprice door sensor P/N 24259. It lists at about $25, so if you wait for a sale it might work for you. (I don’t recognize the model number you listed. But typically if a sensor keeps dropping off the network the problem is the strength of the mesh, not the device. But it could also just of been a bad device. Lots of people use the monoprice sensors, it doesn’t seem to have more complaints than other brands.)

Also remember that for many of these devices, Amazon will not be the least expensive. Instead, you can usually get the best deal by going to one of the specialty home automation retailers. And if you need more than four or five of the same model, contact their customer service and see if you can get a quantity discount. Even if it’s only 5%, every little bit helps. :sunglasses:

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JD, thanks for pointing in the direction of the dry contacts thread. That was useful.

Having said that, good sir - I can neither recognize nor agree with your characterization of purchasing electronics on Ebay. The FUD casting is palatable and compels a rebuttal:

Fact of the matter is, the hundreds of sellers I’ve bought from over the years do their utmost to deserve your positive review and discounts are easy to obtain: It’s called the Make An Offer button. Besides: Ebay has stringent measures and a money-back guarantee to cope with the few eventual rotten apples, who won’t do a return or refund. I’ve never lost a dollar on a bad purchase. Either I got a new device or a full refund.

Sure, if one craves nothing less than the perfect, purist experience in every commercial transaction with the patience of a six-year old - if your world comes crashing down at the mere thought of occasionally dealling with receipt of a defective item., then yes - you’re probably better off staying away from Ebay. Pay more. Be happy.

As for counterfeiting. Dude… it’s not like we’re out buying Luis Vutton bags here, lol. Who cares what box it comes in or if it even comes in one. Either the thing works or not. Should the latter be the case, you get a refund or a new one sent over. Easy-peasy, perhaps Chineesy :laughing:

Doing homeautomation on the cheap is nothing to be ashamed off and there’s absolutely no challenge in buying overpriced products. Now, back to our regular scheduled programming…

Counterfeits present three different problems.

First, they almost always lack the safety certifications that electrical devices should have, and can create a very real fire hazard.

Second, they won’t necessarily do everything that the originals do. I’ve seen counterfeits that had, for example, a fourth-generation zwave chip instead of a fifth generation. That makes a big difference in network performance.

And the warranty issue is a real one.

And it’s entirely possible for someone to buy one of these devices, have one of the first two problems and not even realize it, making the eBay guarantee moot. We’ve had a couple of people even in this community report buying something off of eBay which turned out to be a different model than the product description. Sometimes the seller isn’t even aware of the differences, and simply copies the description of something which looks similar to the item they have to offer.

Obviously, it’s a matter of personal choice. But it should be an informed choice. Without ad hominem attacks. Just sayin’… :wink:

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Hi all, just a quick update on this topic.
Having tested a couple of el-cheapo contact sensors, here’s what I’ve found out so far:

Neo Coolcam - Tried with two of these sensors i got of ebay, however none of them seem to be able to pair with the hub. The ebay seller was kind enough to send a second unit to try out, yet none of them can be discovered. Me thinks they may be meant for another proprietary z-wave implementation, kinda like the Iris Gen 1 smartplugs. Anyway for the record, the friendly ebay seller, was nice to offer a full refund and I didn’t even have to send the non-working sensors back. Easy-peasy, quite Chineesy! :wink:

Sercom SZ-DWS04 - I had much better luck with this device. Available for about $13 bucks, CR2 battery included. Think I just found my favorite hackable contact sensor. The Sercom pairs nicely with the ST hub, although you have to go into the IDE afterwards and manually select the stock “Z-Wave Door/Window Sensor” device type, which will let you read the contact and battery level. I don’t know if this device has more sensors onboard, but at this price… meh.

Opening up and modding it - real easy: Just pop the back cover off, remove the battery and using a boxcutter knife or pry-tool get the inside cover off, allowing you to remove the circuit board The glass reed relay is on the backside. Remove it if your want. Either way, solder a couple of wires on the terminals where it’s connected. Drill a small hole for your wires in the enclosure, right around where the notch is and you’re done.

First project I used this for was smartifying my dumb doorbell. When the button outside is pressed, chime’s screw-terminals gets 6V AC from a transformer somewhere in the house, triggering the ding-dong solenoids. I’m sending the AC through a diode/rectifier bridge and into the coil of a 5V relay, connecting the wires from the Sercom to the common and normally-closed relay terminals. The rectifier bridge converts the AC to DC, preventing the relay from buzzing, tripping the contact sensor 500 times and making Webcore vomit dayglo when someone hits the doorbell. PS: If you’ve got a really jittery relay, add a 220uF capacitor in parallel with the relay coil. For my next project I plan on using this sensor with an LDR resistor to monitor the refill LED on my water softener.