The sensor itself looks like this, in front there is a blue indicator LED. I bought it for the test, although I https://jiji.ng/74-turkeys imagined in advance with what nuances it works. Two AAA batteries are inserted into the sensor, the manual says that the minimum voltage is 2.7v, which means that two batteries of 1.2v each cannot be installed. Sensor dimensions 70x25x20mm. A small review of probably the cheapest wifi door open sensor for smart home systems based on Tuya Smart (their second name is Smart Life), for which scenarios they can be used, for which there are nuances. The cheapest is I mean that its price is constantly dancing, from 5.6 to 7.1 dollars on average. Plus the addition of a similar motion sensor. The sensor comes in a small box, the sensor itself, a reciprocal magnet, a small manual and a paper clip to reset the sensor are available. On the side there is a single hole for resetting the device or linking it to the cloud This is what this sweet couple looks like: sensor magnet For example, now its cost is 5.1 dollars apiece.

Wifi eMastiff TY01 door sensor for smart home Tuya Smart (aka Smart Life)

There is a removable platform at the back with an indication of the orientation, it must be mounted, for example, on the door and the sensor itself is put on it