I dont know if you have used this product before but I have used it for 2 years and only replaced the battery one time! They are really accurate with temps just dont let them get wet and they will stick to any surface!
Jann, a sensor that big might not be the best to put in cage.
For the same price (25 bucks), I would recommend a temp gun instead.
Very very effective, much more accurate as you can even measure your chameleon's skin temp while basking.
We have one similar to this in every one of our cham/reptile rooms for general readings. We do use a temp gun also for more accurate cage-by-cage readings, but I like having it anyway for "room" readings.