The instructions in the comment of activea should be followed in order to connect to mi home. "It is done by pressing 3 times on the mi hub (activating the search for a new device) and then long-clicking on the water leak sensor for 5secs, which automatically pairs the devices and finally the sensor appears in the Mi Home App!"

I had bought 4 sensors for 12 to 13 euros (offer price from a foreign store) about 4 years ago. The build quality is excellent, there has been no alteration all this time, their size is quite small and discreet, and I find it very convenient that the top part is made of flexible plastic, which, when pressed for a few seconds, enters pairing mode with the Hub, making the sensor connection a breeze. In all these years, I replaced the battery once a year ago, so I consider the battery life to be more than sufficient, definitely more than the one year claimed by the company. The device itself cannot do anything, it is Zigbee technology, and you will definitely need a Hub to connect it to your mobile phone. If you have the round Aqara Hub, with LED lighting and a speaker, you can set it to give you a visual or audible signal when it detects water leakage. Of course, you will also receive notifications on your mobile phone when you are away from home. The best option would be to have a shut-off valve in the main water supply, so that in case the water supply needs to be interrupted, because notifications are good, but when you are away from home, things get more difficult no matter how quickly they arrive. This could possibly be achieved with an Aqara switch, like the Aqara T1 Smart, but since I haven't tried it myself, I would suggest contacting the company for more information. Finally, I would like to mention that the Aqara Hub does not have the best range, especially when there is a structural element like concrete in between, and it should be placed in a central location for the best coverage. I consider 25 euros to be a bit pricey, around 17 to 19 euros would be a more "value for money" option, but on the other hand, a potential property damage might make the purchase worth it.

For those who have dealt with "Smart Home programming", I would like to add a couple of things. I used several Aqara sensors through Node-Red and a Raspberry Pi to communicate with a smart home system that I have. The Hub I had was the Chinese version, there was no European server connection available at that time, and I had connected it to the Xiaomi Mi Home app. There was a hidden menu in the app that showed the ID of each sensor and everything worked perfectly. Recently, I wanted to connect some additional sensors, but this menu was no longer available. In a communication I had with Aqara, they referred me to Xiaomi, and Xiaomi told me that they would look into it, but after months passed, I decided to delete the Mi Home app, reset the Hub to factory settings, and then connect it to the Aqara app, hoping to find a solution to my problem. The Hub, although the app detects it, does not connect to my Wi-Fi, and I got frustrated after spending many hours trying to find a solution, which led me to purchase the Conbee 2, which recognized all my sensors and seems to have better coverage than the Aqara Hub. Of course, I cannot yet give an opinion on its stability, as I have only been using it for 10 days, I just mention it for all those who have been more involved in the "Smart Home" and the integration of various technologies and companies.

Although I couldn't connect the sensor to the new Xiaomi YTC4044GL Smart Home Hub through the Mi Home App, I managed to do it by pressing the mi hub three times (activating the search for a new device) and then holding down the water leak sensor for 5 seconds, which automatically pairs the devices and finally the sensor appears in the Mi Home App!! Luckily, I didn't have to buy the Aqara Hub additionally!

I have it here for about 2 weeks. So far, it works very well, indicating when it detects water and when any leakage problem ceases to exist.
Although it states that it is not for outdoor use, I have it on the balcony in a shady area (the instructions mention a temperature lower than 55oC) and so far it works very well.