I was reluctant to get this, but my chihuahua would not stop digging out. Maybe I shouldn't have named him Drifter, LOL. But it is probably as small as it can get and still work, and you can use other cheaper batteries and replace them into the battery holder. You have to snap off the black plastic ring, but save it because you have to set it in the exact place it came off in order for the battery to go back in the slot. And do not trust the flasher, it would flash red at me and then change back to green for a week. I got almost 2 months out of the first battery. So I wish I didn't have to use it, but i am glad he is not running the neighborhood any more. This collar worked fine with our existing wiring and system for our large dog, who dug out last week when I realized his battery was dead. But that battery lasted over a year.