Tia Wyze team, as a suggestion, consider to ship the sensors with the battery isolated, because it comes almost out of energy. I bought some sensors before a got my new apartment and, sadly, few month later I start installation and had to change all batteries: contact sensors survived but motion sensor is dead, not even the LED lights up when the battery is connected.
Other brands use a small piece of plastic that one have to remove before using. In Wyze products, you can make a small groove like cut to the case, where fits a plastic insert to isolate the negative of the battery.
They ship the contact sensor with the sensor and magnet bound together with plastic. I believe they use extremely small amounts of power until the magnet moves away (and back) from the sensor. This wakes them up and makes them use power to send their status.
The motion sensor I can’t remember how it came, but I want to say the front was covered, so that no motion could be sensed. As long as it doesn’t see any motion, the battery usage is extremely low.
But your point is well taken. I will admit I was surprised to see the battery already inserted and running.