Onvis CT3 Door and Window Contact sensor review


Onvis is jumping onto the Thread bandwagon with an update to its contact sensor, the CT3. The Onvis CT3 door and window contact sensor is as its name implies, it’s a contact sensor that works with HomeKit Over Thread.

While a door and window sensor is not the most desired device or one that a HomeKit user would jump for. It’s still good to see other options on the market with Thread support. The other options are the Eve Contact sensor which works with Thread and now Matter. But you also have the Aqara Contact sensor, that requires the Aqara Hub and will soon support Matter.

Let’s now jump into all the details about the Onvis CT3 contact sensor and see it perform with the addition of Thread.

Design and features

The Onvis CT3 comprises two components: a larger main sensor (30 x 46 x 15mm), with all the smart parts inside. The other component is much smaller (12 x 26 x 10.5mm) and features a magnet and both have a double-sided sticker on the rear.Onvis CT3 contact sensor design

Onvis has stuck the HomeKit setup code on the main sensor, but you can peal this off. But interestingly also put a small version on the side of the device along with the serial and Mac address details. At one end of the device, you also have the reset hole.

Onvis CT3 door and window sensor uses Thread, bluetooth low energy 5.0 and CR2450 button battery. Onvis claims will offer 1 year standby time when using Thread connectivity.

The Onvis CT3 smart door and window sensor does not need any Hub or Cloud, but if you want to take advantage of Thread. Then you will need a HomePod Mini or the Apple TV 4K to act as a Thread Border Router.HomePod mini review

In the box, you also get some spacers that are designed for a door or window where the different parts of the placement area don’t align for whatever reason. These allow for the magnet and sensor unit to be aligned correctly.

Based on looking at the previous generation, the CT2. Onvis has taken onboard feedback around the logo size and placement. Finally, and probably obvious to some, the CT3 is not waterproof, so can only be used indoors.

Onvis CT3 Setup

Getting door & window sensor up and running is easy and straightforward. Both the sensor module and the smaller magnet component have peel-and-stick backings. So all you need to do is attach one piece on the door or window and the other on the trim. Just make sure that the alignment markings on each piece line up with each other.

You may need to use the included spacers depending on your area of placement, but its doubtful you will need to use them all.Onvis CT3 install

The final step is setting up in HomeKit, which you need to open up the Home app on your iOS device and add the accessory. You do by tapping the + sign and then add an accessory. Then, start the pairing process by scanning the HomeKit code and following the instructions.

I installed the Onvis CT3 contact sensor on my bi-fold doors in about 10 minutes. This was from opening the box to having it working in HomeKit. This for me is a major selling point of any HomeKit accessory.

Onvis CT3 in HomeKit

For viewing the status of the device, it will appear on the top of the screen with the status. If you long press on the sensor icon, this brings up the settings section for the CT2 in the Home app. In this section, you get the option to change the name of the device, current status of the sensor and battery level.

You also get options to change the type of item the sensor is attached. With the options of Blinds, Contact Sensor, Door, Garage Door, Window. From there, each option has different icons you can choose from to represent the sensor type you’ve chosen, except for Contact Sensor.Onvis CT3 contact sensor HomeKit

I chose the double door icon as I had attached it to my bi-folding doors to check if I had left them open. I was out of the house.

In terms of control and on the most basic level, you can set Onvis CT3 to trigger HomeKit notifications whenever your door or window opens or closes. Using the Home app, you can decide whether you’ll get the alerts all the time, only during the day, only at night, or at specific times. You can also choose only to get notifications when someone is home, when you’re home, when you’re away, or when nobody’s home.

HomeKit Automations

To make more use of the Onvis CT3, you add the sensor to a wide variety of automations. For example, the sensor could trigger a lighting scene when you walk in the door. Another option would be to make the sensor turn down your HomeKit enabled smart thermostat when a window is opened. The final idea is to change the colour of a light to warn you that the sensor had been tripped.

Onvis CT3 HomeKit over Thread performance

The biggest feature of the Onvis CT3 is the ability to connect via Thread to HomeKit and based on my testing, it does this very well. The speed in which the CT3 reacts is fast and based on my testing, I have had no issues with dropped connection or slow response.

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To ensure I got a good understanding, I tested this without the sensor attached to anything and controlled the opening and closing. The speed in which the CT3 reacts is fast and based on my testing I have had no issues with dropped connection or slow response.

I then tested it on my door and again, no issues with response times and connection. It just all worked as expected and it did the job it was designed todo.

Onvis App and device maintenance

The Onvis app is basic and reading the reviews before I installed I was opening it was going to be better, but its not,

At its basic level, it shows you if the sensor is active and either open or closed. Then taping on the sensor icon you are presented with other details. These are connect method, the battery status and a logs menu.

At the top of the screen you have a settings menu option and tapping this reveals details about the device like firmware updates, Thread connection details, state of the sensor and more detailed battery status.Onvis CT3 contact sensor app

Going back to the device main screen, you have a logs menu and this is supposed to present a log of open and close states. But this does not appear to be working correctly. It showed a random number of 114407 and I have certainly not opened and closed it this many times.

Overall, the Onvis app is below average and it could do with a redesign and bugs removing.

Battery replacement

To ensure I looked at everything, I also replaced the battery and I don’t think they thought this through. Remember when I said Onvis had stuck a label on the side of the device? Well, you need to peal this off to open the case. This would not be an issue, but the glue used on the label is not great and it didn’t stick back on very well. So if it’s on something like a door, then it could fall off.Onvis CT3 sticker

Its details like the app and design choices that some users could measure Onvis on. When you compare to brands like Eve and Aqara that focus on the details and delivery solid apps. Then this sets the benchmark and I think Onvis really need to focus on the details.

Onvis CT3 contact sensor review summary

When I first saw the Onvis CT3 sensor, I thought it was on the large size and this was based on the marketing materials released by Onvis. But having the device in my home now, its not that big. The setup was a breeze and the fact I got the device up and running in around 10 minutes is always a positive.

The standout feature is Thread support, and this works great with no noticeable delays or issues with losing connection. Although it is a shame that the Onvis CT3 will not support Matter. Which is a downside for people that want multiple smart home ecosystem in the home.

But little details like the sticker not going back on correctly after a battery replacement and the Onvis app not being great slightly impact an over-wise good product.

Other options?

As already mentioned, the Onvis CT3 has other competition at the time of this review: 10th January 2023. The Eve door and window sensor that works with Thread and recently been updated to Matter at the time of this review, it is only £5 more. I have the Eve also in my home and its rock solid.

Then you have the Aqara contact sensor, which is smaller, cheaper at around £16. Plus it supports Thread via the Aqara M2 hub.  But with the Aqara you need that additional hub, so thats extra expense. But if you already have Aqara devices in your home its a strong alternative.

That being said, the Onvis CT3 is a solid device and does what it says on the tin. Yes, it does not support Matter and they poorly put together the Onvis App. But if you are in a HomeKit only home, then none of these features should distract you from a good product. Plus the Onvis CT3 is very competitive at £29.99 for £29.99 for a single pack single pack, but if you want better value, the Onvis offer a two pack option for £39.99.

So that’s a wrap on the Onvis CT3 contact sensor review and hopefully you have found it useful. Don’t forget to subscribe for more HomeKit and smart home reviews. If you have a question or a comment, then leave it below. You can also follow us on TwitterFacebookYouTube and Instagram.

Onvis CT3 Door and Window Contact sensor review
  • Overall - 88%

Review Summary

The Onvis CT3 is a solid device and does what it says on the tin. Yes, it does not support Matter and they poorly put together the Onvis App. But if you are in a HomeKit only home, then none of these features should distract you from a good product.


  • Thread connection
  • Compact
  • Competitive price


  • App lets it down
  • Some design issues


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