What make was the new battery? I had this when battery got low it started false reading and then just stopped.
The ST motion sensors require Duracel or panasonic batteries they won’t work with anything else. I bought another make and it didn’t work. The shaping in the case must be very specific. Once a duracel was inserted everything worked again perfectly, very narrowly through them away and bought new ones.
This has been seen on other posts. Might be truly dead but you never know.