If trim obstructs the button on the sensor cover, you won’t be able to change the battery. The issue can arise when mounting the sensor on a casement window. If the sensor is mounted on the trim at the very corner, the button will be inaccessible if the button faces the corner. 
I caught the error in time, but only because I had used the button when installing another contact sensor. Please consider adding something along the following lines to the next update of the installation instructions and videos: “Mount the sensor so that its button is accessible. That’s for changing the battery.” Thanks.
