1. The transmitter is expensive
2. The circular pattern of transmission for the indoor transmitter is often not appropriate for the area of containment. How would you use one transmitter to keep an animal off a couch while allowing them around the couch, for example?
3. The thing is big, ugly, and in the way. Where can you put it that will be convenient for you and still will outline the area of containment?
Ready for some good news? We can make our own transmitter, completely compatible with PetSafe collars but smaller than PetSafe's, with an antenna that can be any shape or size, for under $5! Our transmitter can serve as a replacement for an outdoor or an indoor system. And if you are ready for a break from the Arduino and friends I have more good news: we don't need a microcontroller. This can all be done with a couple of 555 timer ICs (available literally everywhere, including Radio Shack, Jameco, and All Electronics) and some supporting passive components. There's no code to write. You can build this thing without ever going near your computer (assuming you have a way to read this and surf the web without a computer.) And you can have the satisfaction of knowing you built the magical transmitter yourself.