This is the manufacturer:
http://squirrel-free.com/birdfeederproducts.html. They have been around a long time. I bought my first one, a 12 port, at Wild Birds Unlimited in East Cobb. The franchise owner is very helpful and does free or cheap repairs on feeders he sells. He made me a test light for the Wild Bill which is handy for checking the battery. Wild Bills are easy to buy. Amazon, Ebay, direct from the manufacturer. The 8 port, which I have now, is big enough.
they require some maintenance. I can completely disassemble it in just a couple minutes. Every 2 or 3 years you have to clean connections with a small wire brush and sandpaper. The manufacturer sells every part should you need anything. My first one lasted about 10 years. They have since been improved with a sealed circuit board which cuts down on maintenance.
They will get your attention if you forget to turn it off and touch the tray and a perch. The roof also has a hot spot, a metal disk. It is also effective against any other pests, rats, coons, possums. Just not birds. They use a single 9V battery which lasts a few months.