Review: Onvis CS1 Security Alarm Contact Sensor

I have been using lockdown and everything related to that to work on the home security system that I am building using HomeKit products. One of the things that I wanted was a way to have a siren using the HomePod Mini that I have. But that’s simply not possible. Apparently if you want to have a siren sound play when for example a motion sensor detects motion, you can’t unless you have an Apple Music account. That’s a #fail. So I went looking for a second option. The thing is, there’s not a whole lot of options out there. As a result it took a while to find a product that I thought would work for me. And that product was the Onvis CS1 Security Alarm Contact Sensor. Here’s what you get in the box:

Besides the two parts of the sensor, you get 2AAA batteries, a pack of three screws, 3M double sided adhesive, and of course the usual instructions, which I should note that the English isn’t the best in the supplied documentation.

Now, let me get this out of the way right up front. This device uses Bluetooth LE 5.0. Which means it only works with your phone in range of it, which of course isn’t practical for this use case, or with a HomeKit Hub (An Apple TV 4 or above, HomePod or HomePod Mini) that is within range. That’s due to the fact that if it had WiFi, the batteries would drain pretty quickly. But the batteries should last about a year or more via Bluetooth LE 5.0. In my case, that forced me to buy a second HomePod Mini to make this work as my HomePod Mini as in the bedroom, which made it too far away to be useful. The second HomePod Mini now lives discreetly in my living room plugged into a uninterruptible power supply. And as a bonus it is part of an active/standby scenario where if one of the HomePod Minis become unavailable for any reason, the second one will take over running my HomeKit gear.

Setting this up is typically HomeKit easy:

  • Take out your iPhone and open the Home app.
  • Click the “+” and click “Add Accessory”.
  • Scan the HomeKit code on the side of the device.
  • Follow the prompts and you’re done.

You then have to mount it. You can use the double sided 3M tape. Or you could screw it in. I would screw it in if you can. Here’s how the finished product looks:

In my case I used the double sided 3M tape and I drilled a bunch of holes to screw it in place to ensure that it was secure. I also placed it at the top of the door for one other reason that I will get to in a moment.

Now you get a number of sensors as part of the deal:

  • Temperature sensor
  • Humidity sensor
  • Door sensor

So in short, besides being able to sense if the door is open or not, it can also monitor temperature and humidity. Those last two features aren’t really useful to me. But they might be useful to somebody else who is interested in using that information to drive automations for smart thermostats for example. You also get a 120 dB siren as well. Though in my testing it did only hit 89 dB when I tested it with my Apple Watch with the volume cranked up to max.

Once you set this up, you can use the Home app to do a very limited amount of customization. You can set it up to arm when you leave, and disarm when you come home. You can add the sensors to automations, and…. that’s about it. To do anything interesting, you need the Onvis Home app which allows you to customize things like the volume of the alarm, the delay before it alarms, and the like. The good thing about the Onvis Home app is that it reads your HomeKit data to allow you to customize it. That suggests to me that you can set this up as HomeKit only and in theory because it is Bluetooth only, it won’t be a security risk on your network. The Onvis app is also used for firmware updates as well. I will say that the Onvis app is a bit sketchy in terms of the user interface as some stuff simply doesn’t work the way that you expect it to, and has some borderline amateur level graphics. Fortunately you can choose to use another app like the Eve app for example which allows you to do everything that the Onvis Home app does minus the firmware update part.

Gripes? I have one. The battery compartment holds two AAA batteries and is unremarkable except for the fact it’s really easy to open and close. Too easy. I can see a situation where someone does manage to get into your home, but isn’t deterred by the alarm and is quickly able to deactivate it by taking the batteries out very fast if he can find the sensor. Your neighbors would likely see that as a false alarm and not call the cops. Then the scumbag thief can go to town on your place. While you would get an alert that the door had been opened, if you’re not close to home you are still in trouble. Because of that, you have to hope that the thief in question hears the alarm (which is very loud and hard to miss in my condo) and decides to run away before the cops show up. Onvis should really fix this by having a screw or some other mechanism to make the battery section harder to open. My own mitigation strategy for this issue is to place the sensor at the top of the door so that it if this situation happened, it would take just that little bit longer for the thief to find it. Which may encourage them to run away instead of trying to disable the alarm.

The Onvis CS1 Security Alarm Contact Sensor goes for $27.99 USD. Which is a pretty low price for this. I’d give this a look if you live in a condo or apartment and you need an alarm system to protect your property. Just make sure that you have a HomeKit hub nearby so that you can get alerts when you are away from home.

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