They hit $10 every so often - if you just need a handful I would buy now, if you need a whole house worth and you’re not in a hurry, keep watching…
The Visonic sensors are a good deal and work great mostly, but seem sensitive to certain conditions.
I had one on the door right next to the ST hub (within 18 inches). It chewed up batteries, then fizzled. I replaced it with another Visonic, and the same happened to that one!
The sensors can be brought back to life by the standard reset process… but if the position is within a couple feet of the hub (necessary in my home configuration), they apparently do use batteries more quickly than in other locations.
Strange, I have not experienced this. I have two located three feet from the hub and another 3 about 6 feet from the hub and they have no issues with battery life. Current batteries are 1.5 years old and still going. If anything, the one have I have furtherest from the hub is draining slightly faster.